Let's say that the guys in the Civil War never seemed to have much problem running around with pouches of caps hanging off their belts...if all that jostling and bouncing wouldn't do it, then I doubt much will.
As far as I know, it takes more than simple impact to ignite a properly-made cap. It takes an actual impact and pressure (crushing) to ignite the compound. That's why it's important to have an "anvil" for the hammer to crush it against. You could toss a cap in the air and swing a bat at it, and I doubt it'd go off...the thing just isn't heavy enough. Even a cap not set all the way onto the nipple won't go off reliably, because it's "cushioned" by the extra travel. It needs to have all the force suddenly applied over a fraction of a second to go off.
Of course, it's good to treat them with care, as they ARE potentially dangerous as any impact-sensitive substance is, but I wouldn't worry to much about it. It's not nitroglycerin.