I considered my son a "grad", when he would tell me consistently when he had to go. I didn't have to watch for subtle signals anymore and didn't have to remember when he peed the last time. If after 4 hours of not peeing he did not ask, he did not have to go. Getting to the toilet in time had become his responsibility - he could enlist my help for taking him there, helping with pants etc. but the "when" was not my job anymore.
Wolfgang was at that point at 20 months. We would still have an occasional accident when he was very busy playing - but that also happens to potty trained 4-year-olds occasionally.
Jutta is no grad yet, she's been completely diaperfree for 8 out of the 15 months of her life now (more than half of her life!!, but i still rely on intuition, timing etc., occasionally she tells me by making a "pffft"-sound.
Outings were the times where we actually almost never had accidents. In your place I'd really give it a try. Take him potty before you leave. Plan pit stops when entering a store or at his usual intervalls. Take extra pants, socks, maybe shoes and just in case an extra shirt along. If he has an accident after all, it's no big deal, you do the same you would do if he spilled a drink over himself, if he sat down in a puddle etc