Wow, three weeks. That's a long time to be in a hotel by the airport.
If I were you, I would try to do the following:
When you arrive, take a cab or bus to the nearest grocery store and buy the following:
--Canned black beans
--Canned diced tomatoes
--Pre-cooked or frozen brown rice (if possible; Trader Joe's carries this, other markets might also)
--Canned vegan chili (if you can find any that's super low in fat)
--Any and all fruit and fresh veggies that look good.
Bring with you:
Spices (including chili powder, curry powder, etc.), nutritional yeast (if you use/like it)
Potatoes cook very well in the microwave and then keep well in the fridge in ziplock bags. They make really good snacks.
I would make oatmeal every morning and eat some fruit.
For lunch I would do the best I could at the cafeteria to have a big salad and whatever else looked decent. (I'd probably bring a cold cooked potato with me as well.)
For dinner you could make the following things:
--Curried lentils over rice w/ veggies
--Black beans and salsa over baked potatoes w/ veggies
--Chickpeas and tomatoes (possibly curried?) over rice or potatoes
--Steamed veggies with noochy-mashed potatoes