|Bottle caps are the de-facto currency in the Equestrian Wasteland.|
~ Bottlecaps by lcponymerch
|Sometime after the end of the war, bottle caps rose to power as the standard form of currency in the wasteland. While pre-war currency still holds some value, caps from Sparkle-Cola and Sunrise Sarsaparilla bottles are used to supplement the wasteland's barter economy when purchasing goods or services. Bottle Caps are also used as shrapnel in homemade mines to cause additional damage.||
While caps are the primary currency in the Equestrian Wasteland, pre-war money, or "bits," still hold some value as they can be used to retrieve bottled beverages and ammo from ancient vending machines.
It appears that bottle caps have no actual mass and are quite small, as ponies are able to carry thousands of them with little trouble.