True, but I still figure that losing a couple percent in rewards beats doing a high-street currency conversion.

Although anymore I rarely have much foreign currency on me at all. If it's under $50 worth, I just take it home so I have a little in my wallet at the start of the next trip. If it's $50-150, I pay cash for some regular expenses on the last day...the cab ride, lunch at the airport, etc. If it's $150 or up, then I use it for the hotel bill.

Most airport duty-free shops can also split payment. That's another option if you're in the $100 and under range. I've overheard people in shops before saying something like "I need to find an item that costs exactly 19 Euros"...not aware that they can purchase anything, hand over all of their currency, and then pay the remainder with a credit card.