I feel like things are pretty good here. After one day in diapers (all the trainers were in the wash) we had a big set back. We went from 1 accident a day to 2-4 accidents a day, and bigger ones too. Definitely not going to back diapers again! That was about a week ago, he seems to be back on track now. We've even had a couple of completely dry days! We'll still have an odd day with more accidents, I'm trying not to focus so much on the day to day progress/regression but on the overall arc. Still wearing diapers to bed, but he's now had 2 nights where he stayed dry, and he asks to go potty occasionally in the middle of the night now, so hopefully the night time dryness will come soon.
As far as errands, I always take him before we leave, but he always asks when we are gone. I think he likes to see all the different bathrooms, lol. We had a week or two when he would ask when we were out, and I would take him but he couldn't figure out how to go. But I just kept taking him, because we didn't have any other options, he was also still in diapers then so it wasn't as big a deal to miss. I was trying to find one of those folding seat reducers, but right before I bought one online he figured it out. It just took one time of actually going in a big potty before he could do it reliably. My biggest problem is that not one of the playgrounds near us have bathrooms. I've thought about having him pee in the grass, but I'm just not sure if I'm comfortable with that. So I make sure we leave for the park right after he's gone and then cross my fingers and head home while telling him to hold it if he asks to go while we're there.
My sister is babysitting him for me tonight. I hope he feels comfortable enough to let her take him potty! She's never babysat him, though we've hung out all together with her before.