Don't leave home without another card. ;-)

Actually, if your credit limit is, say $5k, you can only buy $5k of stuff at a time. Once the purchases post, assuming that you have prepaid your account to cover all your purchases, you will be able to buy another $5k. So it can take many days to buy lots of bonds, even if you send in the whole payment ahead of time. I don't know why the credit card issuers do this, but they do. The only real relief is to get a higher credit limit.