Upload & Sell: On
I try to ensure that I always have enough cards with me. The few times I've had to do it, it worked OK, but that's rare for me.
P.S. If you've been doing it for years, then I'd just leave it alone. If you're still concerned, then just buy some more cards. There's nothing as self-fulfilling as looking on the internet for people who have had trouble with stuff - any stuff.