It says my bag is full when it's not in Pokemon Silver what do I do?

If your bag is full in Pokémon Silver, it means you've reached the maximum number of item slots allowed, which is 20 for key items and 30 for other items. To resolve this, you'll need to either use some items, sell them at a Poké Mart, or transfer them to your Pokémon's held items. You can also visit a PC and store items in your item storage for later use.