I’m going in the first place for water filters, as soon the water supply stops, you need some way to filter water.
A lot of people will drink anything when they have trust, so I guess a lot of people soon will be sick. So water filters and maybe even a small wood stove made of tins for boiling the water. Not everybody is handy, so the tin stove may look stupid, but believe me, there are people out there who are gonna be happy to buy one when SHTF
Number 2 is fire lighting material, as soon the electric piezo don’t work anymore, everybody is gonna need some way to light a fire in a bigger amount then now.
Number 3 is food, all kinds of, and seeds so people can grown there own
Number 4 is antibiotics, painkillers and medical stuff like gauzes, bandages etc.
Number 5 is skills, learn how to repair shoe’s, clothing and….
Number 6 is wood processing material, axes, saw blades, billhook
I have one concern, my guess is that when SHTF happens, the government (or other looters) will come for your goods.
So having it in a hiding place is probably a good thing.