Stock up on stationery and accessories that you like and come across during shopping sprees. You may not have the time to go out again and buy some if you run out of stock at home. The same designs may not be available elsewhere, and you’ll be left chastising yourself for not picking up a few pieces along the way. That has happened to me. To this day, I’m trying to find a reason to go back to a stationery supplies store that’s nearly an hour away from where I live. (Letter writers can sometimes be obsessed.)
From experience, it also helps if the designs of the items you pick are not too cute or unique (e.g. a commemorative insignia) that you don’t want to part with them anymore. Unless that was your original intention: to add them to your growing collection. In which case, buy some for yourself and double your happiness by sending the rest to friends and loved ones.