We initially used collapsible bowls for Chloe’s food and water at her on-the-road home base (that is, the place where we set up her travel crate and a bowl of water). I’ve moved away from that, because I think small stainless steel bowls provide more stability — Chloe, playing, sometimes bounces perilously close to her soft-sided collapsible bowls. Now I have one tucked into my purse and another in the car’s glove compartment, for emergency use during an errand trip. When we’re visiting a dog park we’ve never been to before, I make sure I have one with me (along with a bottle of water) because the Gulpy I use at home is too bulky to pack for most trips. (I first decided to carry my own water bowl when I saw dog owners at a park in Florida washing their dogs’ paws off in the only water bowl provided — fixed to the ground, so I couldn’t rinse it out.)
I’ve bought (or considered buying) a lot of collapsible travel bowls. Most are just too darned big — Chloe will never weigh much more than 13 lbs., and she eats maybe a half cup of food at a time and only laps briefly at her water. She just doesn’t need a 2.5 qt. bowl. Other collapsible bowls, with more reasonably sized bases, are too deep — she doesn’t want to stick her head into a dark well to reach the modest amount of food or water she needs — but you can sometimes get around that problem by folding the rim of the bowl over.
The one that has worked best for us is Canine Hardware’s Hydro Bowl. Folded, it’s small enough to fit in my purse or a pocket. Unfolded, it’s sturdy enough to stay reliably upright, it’s shallow, and its opening is wide and holds its shape pretty well. (Chloe gets spooked when her bowls close their jaws shut on her muzzle.) It’s also definitely waterproof. The other one we use, Bison Design’s Fold-a-bowl, is deeper, but not too bad; after it has held water for a few hours, though, it feels damp. We use it for food instead.
Here are two more travel bowls that I would order in a heartbeat, if I didn’t already have too many: Trixie & Peanut’s Port-o-bowl, and How’s Your Dog’s “Fold ‘n’ Go” travel bowl. They’re small and shallow, they fold up neatly and they have a handy clip. [8/4/10 I finally broke down and bought the How’s Your Dog “Fold ‘n’ Go” travel bowl, and I’m happy I did — it has the unexpected benefit of being able to enclose Chloe’s dinner in its folds (you can’t zip it closed with food in it, but it folds up around the food well enough to contain it), so I can tuck it, loaded up, in my purse, and then put it down next to Chloe if we’re out during dinnertime. My usual go-to bowl, the Hydro Bowl, can’t do that.]