The problem is that people do not want to wait half an hour for several block confirmations.
No reasonable store will force their customers to stand there and wait for several block confirmations. In the past, most of the stores did not require a single confirmation since it isn't that easy to double spend Bitcoins nor is it a huge risk for a small value item. Currently, it isn't an option, obviously due to the transaction fees.
Will there ever be a world where people can pay with any cryptocurrency in a store? Will we need some kind of smaller 'buffer' wallet, that allows people to buy things instantly with a crypto paycard, so that the actual amount is taken from the address later? What about all these different cryptocurrencies; you can't ask a store to have 500 different wallets.
Just curious if there is a solution to this problem.
Yes. If you use an offchain solution, its instant and free. Examples are Coinbase, Bitpay etc. I don't believe every store should accept all the cryptos either.
Other than that, lightning network would help.