Straight razors: no regrets (even though in triple figures!), I have my favourites (Swedes and Japanese) but I enjoy the restoration, honing and history of others too much also. I get attached to them and can't bring myself to sell
Straight razor hones: no regrets, have a synthetic set which does the job but I enjoy the variety/history of naturals too. High prices on the latter (especially Jnats) have kept me on the straight and narrow to some extent.
Safety razors: regret getting into vintage Gillette, not because there's anything wrong with them (on the contrary) but I just didn't use them (straights took over). All sold apart from the lockable prison Psycho (no jokes please

). I also have the steel Feather DE and the original Mongoose SE - but hardly use them too. I hesitated about keeping the Pils, but having to use a different angle finally got on my nerves
Brushes: regret buying ones with glue bumps and sold them all (but hard to know over the internet apart from Paladin). Down to two Plissons HMW/horn, Simpsons Major and Simpsons Chubby 2 synthetic. Paladin is on the radar.....
Soaps: regret buying too many scented soaps, so much easier to add scent at the end of the shave and you can't possibly buy sets of everything! Now only use unscented: Valobra (still have a stash), MdC, Haslinger and Wickham.
Aftershave: just Meißner Tremonia Pure (unscented), same comment about scented.
Balm: Meißner Tremonia Pure (unscented), same comment.
Fragrance: regret the ones I bought at the beginning because I was impressed by the big brand names (mainly overpowering French fashion house cologne variants), down to D.R. Harris Sandalwood and Acca Kappa 1869. Penhaligon's Endymion is on my radar....