If you're looking by the registers at a drugstore, you'll probably miss the SPF lip balm. Go into the makeup section, and ask for help. The SPF stuff (at least here in the US) is usually mixed in with all the other makeup, and it's sorted by brand, not by what it's for.
Then when you find some, don't just buy one. Pick up at least 3 or 4 so you don't run out easily and always have one handy. The products sold as sold as special for sports are going to be *priced* like it too... and they won't work any better or worse than cheap stuff from a drugstore.