What do you guys pack for lunch and/or dinner?

I've taken a look at my schedule for this semester and it looks like I'll be stuck on campus from 8 AM - 8 PM or so on certain days.

I can't seem to function without food and purchasing food on campus and/or takeout seems like an extra monetary burden on top of all the other expenses you've got to deal with whilst studying engineering.

For those of you that pack your own food what do you pack and how do you prep?