3 day potty training!

First day is complete and he’s peed in the potty quite a bit, along with many accidents of course.

My question is how do I go about this after the 3 days are over.

I know the daycare will help expedite the process but do I just let him wear underwear in the car?

If we end up going out it won’t be till next weekend. So by then how should I proceed?

Thanks a lot for your help...