Depends where you are out and about!

At restaurants and cafes I always give Jett some of what I am having. Otherwise I take things like sandwiches with me and whole pieces of fruit.

Even though it is messy, I have never encountered a problem while out. At cafes etc I spread out a few napkins on the floor and just let all the food drop to the floor. Then at the end wrap it all up and gather a few extra napkins and scoop up all the debris that missed and put it on the plate. Most waiting staff tell me not to worry about it, they'll do it and don't be silly that is what they are there for etc. I do often wonder if they are so nice about it because I do make the effort to clean up.

If you are more worried about clothes etc we have a few 'puddle feeders" from the ABA. They basically look like an art smock with a catcher pocket on the front. They protect him completely from the mess and then when I take it off him I just turn it inside out and wrap it up containing the mess on the inside. They wash and dry really easily and pack down nice and small for going out.