magnesium and zinc.
And vit D, of course.
If you have calcium going into your gut, the ultimate source doesn't matter as long as you are absorbing it. If you can't eat dairy (like so many folks) then go for other high calcium foods or supplements. Ca ions are Ca ions, regardless of whether they come in a pill or in a cheese sandwich.
The associated nutrients in the cheese sandwich are much more exciting than what generally comes in a calcium citrate/vit D/magnesium/zinc pill, which is why most labels I've seen say you are best off taking the pill with a meal. (better absorption)
Zen - just jump. whenever you want. There are some great force-line xrays of hip joints (the head of the femur) that show the different deposition patterns of bones subjected to impact vs bones that aren't. Jump, girl, jump! Get a jump rope, jog, whatever. Get those bones used to impact and depositing calcium where they need the extra buttressing, so that someday when you miss a curb your femur says, "No problem, I touch down like this at least 50 times a day" instead of "OMFG! Impact! I can't handle this! <snap!>" I've talked with lots of folks who swear their hip broke BEFORE they fell. The break caused the fall, not vice versa.
"If Americans want to live the American Dream, they should go to Denmark." - Richard Wilkinson