My view, skip the vest, as suggested by others. I use a fanny pack type thing myself and can carry quite a bit of stuff in it.
I would get the glasses as suggested, even cheap polarized glasses are a good investment for seeing in the water and to protect the eyes in case a bad cast places the fly a little close to his head.
For leaders and tippet matterial, let him know that those little Stren filler spools will work fine and show him how to tie his own leaders. It’s alot cheaper than the mono sold as true tippet material and will be very budget friendly.
The fly line that comes with the kit will work fine to start out but when he is ready to get a new line be sure to point him to some of the better low cost lines.
As for patterns, teach him your go to patterns, such as a streamer pattern or two, wooly buggers, most used nymph patterns (usually bead head hairs ear, prince, and/or pheasant tails), most effective dry fly patterns, and midge patterns, and, if you fish alot of smallies in your area, the value of cheap poppers. The fly’s, even those he purchases himself, do not need to be expensive and going for a huge variety of expensive fly’s, though it can be fun, is not needed.
This part may be jumping the gun a bit, but many beginners start wanting to try fly tying. Make sure he knows that fly tying, though again a fun way to pass time, quite often is not cheaper than buying your fly’s and that if he does decide to get into tying to be sure that he knows again, to limit cost of materials, only the most used fly’s should be tied, don’t waiste alot of money trying to get all the materials needed for all the cool patterns he sees. Most won’t work much better, if any better, than the old stand by’s and sticking with them will keep costs down.