Bottle Caps aren't an effective currency
To be an effective currency it must hold value which is one reason why the American dollar and the British pound are so prolific.
The reason a currency must hold value is because:
If I sold you a chicken today for 3 wibbleys and tomorrow I couldn't buy a chicken for 300 wibbleys I effectively traded something useful for nothing. The only reason we can support a currency is to say this useful item has a set value that will be the same '~over time~'. Then what makes currency advantageous is by saying all these useful items and services have a set value which currency can be used to represent and store that value facilitating trade. (A bit imprecise but this is a very large subject go read it)
As im sure you realize at this point this isn't quite how our world works. which brings us to inflation is when you increase the amount of currency thus devaluing it. If there is suddenly more currency then its rarity decreases, suddenly the chicken goes from 3 wibbleys to 30 wibbleys. Inflation can happen on the other side as well (though by another name). If suddenly you had 300 chickens to the point no one wants them any more, the price of your chicken starts to go down to the point you can have 1 chicken for 1 wibbley. Currency is subject to the same force of supply and demand.
Inflation is the same problem you have, a currency that could be easily forged or found in a shipping container by the thousands would be subject to erratic and controllable inflation.
Anyways, as to your original question. The simple solution is to have denominations. Maybe coke caps are like 1 dollar and a Crush orange cream soda cap is like 1000 (because its more rare).
You could also have banking systems. Promissory notes between banking branches were a huge solution to personal transporting of large sums of money in the medieval ages.