On a 100k ride you're burning between 2000-3000 Cals so of course you're going to be hungry. If you don't want to lose weight you'll need to eat 2000 extra Cals for the day. That will take more than soup and a small sandwich. If you want to lose weight then don't eat the full amount and maintain a deficit for the day.
Eat moderately more food before and during the ride. After the ride is complete eat something for recovery ASAP.
If I do not follow that plan I will eat 2X the calories I burned after a ride.
I have yet to gain any weight following that concept. In fact, I weigh less.
Make sure you eat a good breakfast before your ride, maybe 45 minutes to an hour. I recommend a 400 calorie meal.
During the ride, it depends for me , on how long I'm going to ride. If I'm only going for an hour ride, then I only bring one water bottle with me. Anything longer, I will bring maybe a granola bar, and an extra water bottle.
After the ride, I tend to eat a lot of protein, anywhere from 75grams to 150grams. I usually get it from tuna, peanuts, chicken and beans. I also make myself a protein shake (whey protein). If you follow this plan you shouldn't be searching for extra food all day long. This method ties me down very good.