Is there a way to do more than 1 item using in-app purchase? For example - can I buy 2 of the same item?
No, not at this time. You can buy multiple unmanaged items, but they'll need to be separate purchases.
As a workaround, I've seen people create separate SKUs for different item quantities. For example:
Alternatively, you can allow users to buy in-app credits specific to your app (again, you'll need to create different SKUs representing different credit values), then write your own storefront for exchanging these credits for goods. It's a bit more work, but this gives you a lot more control and flexibility over the checkout flow.