Change feeding routine so that bottles don't have to be heated.
If you're using formula, use the instant stuff. That way, you can walk the parks all day without the "water" going bad and mix it on the spot as needed.
For those breastfeeding (and mommy isn't comfortable feeding in public), keep in mind that fresh EBM is good for as much as 10 hours (depending upon who you ask, others will say as little as 4-6 hours).
Now I realize various people with have specific situations (medical or tempromental) that won't be able to follow this advice. So don't flame me. I just point it out because there are plenty of parents out there that this thought just never crossed their mind. Everytime you see babies being feed on TV, it is/was always a warm bottle, so there's lots of people out there who just never considered the fact that a babies bottle doesn't have to be warm.
[EDIT]
I just reread the OP's original question and realized it was about FOOD and not bottles (sorry, we just had DS #2 and we're still at the bottle-only stage).
But once again, there's no rule that states a babies food has to be heated. If you've already "trained" your infant to expect warm food, obviously you'll have a harder time and my have to try backing off of that BEFORE your trip. For those thinking about taking a trip and will be starting to feed baby between now and then, begin things off with unheated foods.
So for all new parents out there, while it might not be the norm, it will make baby life a little more simpler on you if you start by NOT warming baby's bottle, don't warm baby's food, and use water rather than EBM when you start trying cereal. Again, some people will not be able to follow this advice for medical or temporamental reasons. But for the rest of us, why make parenthood more difficult than it already is?