How can I fit MORE calories into my day?

Yess, I want more calories!
I''m slightly underweight now plus I keep losing and I want to be thick or average sized again.
I usually only get 500 to 1,800 calories a day (I calorie count). I''m aiming for 2,800.
Its hard to find time to eat and I don''t have a lot of food availible.
Ensure and other protein shakes are just too much money.
How can I get more calories in my day? I feel like I''m starving myself to death.
Also, any weight gaining tips are appreciated.

(I''m not particularly worried about health right now, once I start gaining weight I will focus on healthy eating habits)

Thank you and I WILL be choosing a best answer (: 10 points!

10 Biggest Mistakes Made When Trying to Lose Weight

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Wow 500 is low haha. I''m underweight too and am really trying to gain weight so here are some tips:

Peanut butter and milk, a few tablespoons before you go to bed with a glass of milk is 600 calories right there. The milk makes the peanut butter go down really easy, and yes its healthy, good fats and protein for muscle building actually.
Pasta and chicken are good calories, buy some Sidekicks, about $2 each. Good 600 calories per bag.
Oatmeal and yoghurt for breakfast is great

And other than that just eat constantly! Good luck!

• Eat as much of the food you have available as you can stand to in a single day, then do that every day.
• steal sugar packets from a restaurant and have 100 of them per day.
• Milk,milk,milk,and milk. Also do some chicken and hamburger meat. If you can afford it cheap steaks too.
• If you''re super busy, eat during your travel times. Grains like pasta and bread and good for gaining weight. But honestly, the best way to gain weight is to eat junk food. A lot. But you''ll feel like crap and have low energy. But you said you didn''t care about health, so doughnuts, pizza, etc. are the best things for gaining weight
• The best way to put on more weight is to eat more meals throughout the day. And your plan on focusing on eating healthy after you put some weight on is an extremely bad plan and will back fire on you terribly. You should start with eating healthy, it''s difficult to change eating habits, especially bad ones. Eat more complex carbs, like brown rice and whole wheat bread. Eat snacks like celery with peanut butter. Add more olive oil to your meals. Things like peanut butter and olive oil are healthy fats that will help you get to a better weight without clogging up your arteries. And keep in mind that even skinny people can get high cholesterol problems if they don''t eat right. Eat lots of fruits and vegetables and try go eat healthy fats like peanut butter, olive oil, and nuts.
• Eat higher calorie foods. Like nuts, sugary cereals [sugar for high cal, but also have alot of vitamins and minerals]. Drink fruit juice too