Generally, I bring just water and/or a drink. If the pace of play is pretty fast, and I'm off the 18th hole within 3 hours. The fastest round with a cart was a little under 2 hours, and I still had to wait sometimes.
However, my feeling is that snack bars exist for a reason.
Even though it is rare that I get an actual lunch. When I do it is usually a burger and fries which takes about 6-7 minutes to prepare. I usually ask if I can putt out, then get the food ordered. By the time I have teed off the 10th hole, the food is ready for pickup and we did not cost the party behind us any time at all. One might argue that we play slower, but since most of my partners are fast players we usually end up waiting at all the tee boxes. The food is usually gone before the 12th tee, and we are replacing time we would be just sitting around swinging our clubs with eating.
Sometimes I also bring hard boiled eggs, cold cuts and other assorted snacks including peanut butter granola bars.
Damn dude, I need to play in your group. Then again, with all of that food I would probably be asleep in the cart!
I played with some older guys on Tuesday mornings when I had a schedule that allowed me to play in the mornings. These guys would craft some breakfast sandwiches that were fit for kings. I'm talking uncut italian bread, cut in half to form two sides of bread, stuffed with scrambled eggs, bacon, green onions, bell pepper and cheese. I don't know how you guys pack away all of that food on the course lol.
I get a hot dog at the turn and a few beers and I'm good for several hours after that. 80% of the time I regret the hot dog too, especially if it's really hot out. I find it hard to eat when it's 90°+.