Oh good! Warm weather makes it much easier. Yeah, a shoebox with a couple of air holes punched in it and a stick/vine/something for him to hold onto is all you need. I like to line boxes with a little paper towel for easy clean up.
Definitely keep an eye on him, but he should be totally fine until Monday. It's early stage mouth rot, so as long as he's eating, drinking, pooping, and otherwise behaving normally I wouldn't be super concerned in the mean time. There's not too much you can do if he's rubbing due to him feeling he doesn't have enough space, unfortunately, beyond providing him more room. He's of the age when he's probably looking for a mate, too, which may be making him more agitated in general. If he has some sort of free range space, he'd probably appreciate a bit of extra time out and about if possible! I'm afraid I don't have much else in the way of solutions, beyond keeping his enclosure immaculately clean. It may be worth giving his enclosure a good deep clean over the weekend. JacksJill has a good guide to deep cleaning
here, and uses very similar techniques to what we recommend to owners at our clinic. I'm super paranoid about using bleach anywhere near my birds, so I do any bleaching outside and let it dry in the sun for most of the day when applicable- don't sun dry PVC or plastic, as it'll warp!! Since I work at a clinic I have access to bird/reptile safe disinfectants that i tend to use instead of bleach (i love HemaPeroxy!). I'll try to remember to ask my vet if she has any additional tips when I see her in a few hours, if she isn't too busy.

I know she's on her surgical rotation today.
They'll probably flush his mouth out with an antiseptic while you're at the vet's, and prescribe an antibiotic (likely in the form of a cream, possibly oral meds). It's early days, so it should heal up quickly!