Regarding how we pay for items in the pack when we have ISA's and the boys get 100% of the popcorn commission, we handle it through our budget.

In the late summer we determine the schedule of events for the next year (September 1 through August 31).  We also figure out what the projected cost for each event will be and use that information to compile a budget.  We also are sure to include some other costs in our budget such as leader registration, insurance and training costs, our annual charter fee, any other expenses that aren't tied directly to a single event such as rank badges, etc.  We then take that entire total and divide by 50 boys (average number of boys in the pack).  Add to that the cost of registration and insurance, round up to the nearest whole dollar and that becomes the pack fee for that year (add $12 if the boy wants to receive Boy's Life).  That way those things like pack meeting supplies can be covered without the leaders dipping into their own pockets.

If something major were to happen like the Pinewood Derby track broke that we just didn't have the money to cover replacing, we would have to hold an additional fundraiser where most or all of the proceeds goes to getting the money for that one specific item.

As an aside, my personal feeling is that every pack should have this type of issue with having to purchase a big ticket item that isn't normally budgeted (like replacing a pinewood derby track that breaks).  If units are building up war chests of money then they're not spending enough money on the kids who are bringing that money in by selling popcorn or doing other fundraisers.