I am starting to deal with these issues as I move into long rides. We always carry some mini-pretzels. Real pretzels have no fat, tons of salt. I carry a protein bar like Met-Rx with me on long rides, and take a nibble once an hour or so. I like chocolate Gu a lot, but I need to find a flavor I can tolerate that is sold in bulk. You can't even get Gu in the big pak anymore.
We like to stop for a lunch on all day rides. But I have to be careful about what
I eat. I have to avoid fat as much as I can or my tummy gets upset. I usually have a club sandwich (no mayo!) and iced tea, or some soup if it isn't cream based. I have the waitress bring lots of bread to dunk in the soup. Gazpacho on a hot day can be nice. Afterwards we sit and chat for a while to let it all settle.