they rented bikes for 5 days and used them only one day, but they don't care, they paid for the bike rentals with bumpa-bucks
"large sums of money paid or reimbursed by a grandfather to his children or grandchildren for extravagent or unnessary purchases such as vacations, vehicles, clothes, and entertainment
"they rented bikes for 5 days and used them only one day, but they don't care, they paid for the bike rentals with bumpa-bucks" What is the definition of "bumpa-bucks"?