Greetings,
I went to pump up my tires just then and found that both those little screw on valve covers have gone. Did I forget to put them back on last time...who knows, but BAM! they've gone.

So that begs the question, just how important are they? How likely are the valves stems to get damaged if I don't have them on? Should I presume that my LBS would stock them, or even autoshop?

The valves are Shraeder so if I am in trouble without them I can always borrow some off my sisters car until I find somewhere to buy them.