Over at Books, Bikes, Boomsticks, Tamara’s got a good bit of advice up about making sure you have multiple magazines available for your rimfire guns.
There’s really not a whole lot I can add on top of what she’s got to say. Eight or ten magazines is a great number, but if you’re on a budget shoot for a minimum of six. If money’s tight, consider going to your local gonne shoppe and ask to paw through the miscellaneous magazine box. More often than not you’re likely to find at least a magazine or two that will fit your gun, assuming it’s a Ruger, and with a bit of cleaning, they’ll run just fine.