For one thing stop the Kratom. It’s highly problematic in general but weight loss is a common side effect. General stimulation without energy reserves is also a common side effect leading to dizziness.

https://www.mayoclinic.org/diseases-conditions/prescription-drug-abuse/in-depth/kratom/art-20402171

For food try a Shooter’s sandwich.

If you have use of an outlet for an hour or so before lunch rice cooker meals can make a great hot lunch that only needs to be plugged in before lunch.

You want carbs (energy) and protein (muscle). Stack up PB&Js. Dude I worked with in the coast guard would have two triple deck PB&J for lunch absolutely loaded with pb and j. You get your carbs from the bread, the protein and fat from the pb, plus sugars and a small amount of vitamins and shit from the j.

I am by no means expert on the topic but I am also in the same situation as you. If your job is a 12-hour shift pattern, that means you have 3-4 days off in one week. Use those days to cook food and do meal prep for your job, and also to eat as much as you could. Eat food high in proteins and calories. Chicken is the usual go-to meat because it is low on salt and fat, but high on protein and calories. Lean beef is also great. Moreover, it is also important to eat fruits and vegetables to provide nutrients that amplify the muscle intake of proteins, such as spinach, quinoa, lentils, avocado, banana etc.

If you are really skinny though, you have a licence to eat. You could “dirty bulk” by eating as much junk foods as possible to accelerate the weight and muscle gains.

Again, I am no expert but these are what I had been advised and researched on. You should find more information on the Internet.

I worked with a guy who was taking roids to bulk up. He once ate three sandwiches on his lunch break. I am not suggesting that you do the same. It’s just the only thing I have as a point of reference.

Search for sites about muscle building, probably.

I did GOMAD, actually more like 1/2 GOMAD. https://www.healthline.com/health/food-nutrition/gomad-diet for 4-5 months to gain weight. Went to the gym as well, so at least some of the weight goes to muscles.

Trying to eat more is going to be very difficult for you due to early satiety and not knowing how much more you actually need to eat and it is hard to count calories from random food and do math in your head all the time is annoying.

We skinny people think that we are eating enough but actually need to eat a lot more than we think. Maybe our bodies are not efficient at extracting the calories from food or high metabolism, I have no idea. I will be eating the same as my normal/ overweight - friends but not gaining weight. With GOMAD, you can monitor the calories and can figure out at which point (calories) you start to gain weight. The math is easy to do as well.

In my opinion, milk is the most easiest if you can handle milk. It is fast to consume, 0 preparation, easy to monitor/count the calories, easy to adjust as needed and can fit easily in to your normal habit/schedules and lastly no dishes (only cup) to clean up. The more easy something is to do, the more likely you will stick to it.

I built up to it, started with 2 glasses of milk a day, and slowly increased every few days to 1/2 GOMAD. Your bowels will tell you if you are drinking too much too soon. Go slow, the body digestive system, and microbes need to build up to it. Once I noticed I was gaining weight, I stayed at that amount for a few months. It was 1/2 GOMAD for me.

Note that this is not a long-term thing, I don’t think it is healthy long-term. Once you reach your goal, focus more on a variety of food. I still drink about 1 litre of milk a day. One thing I notice is that once you gain quite a bit of weight, it is quite difficult to lose it.

Roasted peanuts are cheap, high calorie, high protein, and shelf stable. It’s a decent mix of all the macronutrients (including carbs and fiber). Personally, I can also eat them all day.

Around me, a $3 jar has 2500 calories, over 200g fat, over 100g protein, and about 30g fiber. On a per dollar basis, it’s hard to beat for shelf stable food.

Get some soylent and take it with you to the job site. You just unscrew a bottle and you can chug 320 calories in a few seconds.

Easy, clean energy. Doesn’t have to replace your meal either. Just something you can ingest very rapidly even if you don’t have an appetite.

In other news, nuts are very calorically rich for their volume. So if you’re just wondering how to get a lot of calories with something you can take on-site, a big jar of mixed nuts can’t hurt. Keep it in your car or break room.

My observation from hiking the Pacific Crest Trail, and also from babies, is that you can burn through your blood sugar in about 2 hours. It doesn’t matter what you eat but target 200-300 calories every 2 hours while working. In a 12-hour shift that might be 5 snack breaks in addition to breakfast and dinner.

I would bring everything you like eating, like a big snack bag, and just eat what looks good for 10 minutes. Potato chips, Cheetos, Nutter Butters (or other cookies), dinner leftovers, trail mix, candy bars, fruit snacks, cheez-its. I like Pro Bars for their caloric density. For breakfast whole milk Greek yogurt has a lot of protein. Smoothie or with granola & seeds/nuts.

Why on earth are you eating kratom at work?

Rice and beans

Chicken (season and cook on a pan in the oven at high temperature)

Make soup

Stew (thicker soup)

Oatmeal for breakfast

While you’re bulking: pasta and bread

You can cook diced onions and other vegetables and add to pasta sauce to improve it

I like to make up pasta dishes in sauce with veggies that reheat well. Pasta alfredo (made with butter and parmigiano reggiano) with spinach and pieces of chicken, or red sauce pasta with a bunch of veggies like zucchini, broccoli, onions and even beans, with some olive oil in the sauce. I buy the precut frozen veggie medleys and chuck them in. You can also make egg fried rice with veggies in it, with your choice of butters and oils. Cheese, nuts, dairy, eggs, I agree with other commenters that fat is not your enemy. Sugar and ultra-processed stuff should still be avoided but embrace the butter, haha.

Peanut butter is also fantastic for healthy calorie density and travels well.

When trying to gain weight (or simply not go minus as in your case) the method will be the opposite of what is needed to lose weight. I have helped someone with this in the past and what I saw as his greatest trouble was that he would get too full to eat more very quickly. I asked about his diet and it was just full of foods which are very filling without actually containing many calories. Lots of fruits and vegetables with almost no carb and no fat.

So really what you need are easily digestible and not too filling calorie rich ingredients. Think lots of grains and fat. Buttered potatoes instead of air fried potatoes. Carrots instead of lettuce. White pasta over whole grain pasta. Cream or mayo based sauce instead of a stock/water based sauce etc. However still try to eat healthy. If going for bread take the white bread without added sugar for example. And still include vegetables but don’t make them over ⅓ of your plate. I have read many success stories with adding heavy amounts of dairy to the diet which makes sense since milk is there to grow a calf as fast as possible. Drinking a package of milk a day is almost a miracle cure to being underweight if you can stomach it. In fact the medical food packs they give to malnourished children are dairy based. Consider it if your diet allows it.

However what specific meals which are convenient to bring I don’t have many ideas. But I hope this mode of thinking will help at least a bit. It has to be a big portion that you can actually stomach. Think about which foods you seem to be able to eat a huge amount of and then narrow those down to the most calorie rich. They also have to not clog your stomach for the whole rest of the day so being easy to digest is also key.

If you’re not sure about something, rub it against a piece of paper! If the paper turns clear, it’s your window to weight gain.

The easy way to add calories and protein is dairy products. Start your day with coffee and heavy cream instead of milk or half and half. Add cheese or butter to meals you already enjoy.

When a buddy of mine was general labor at a warehouse, his lunch was occasionally a sleeve of Oreos and ice cream. You can be as “irresponsible” as you want for a while.

My bulking food was always Triscuits and hummus. A lot of calories in a small package and not really unhealthy. Walnuts are also good for you and calorie dense.