Plan spending on concert and event merchandise.
Merch stalls are impulse environments, so the useful number is a price ceiling per item decided before you queue. Pegging the merch budget to a share of the ticket price keeps it proportionate to the event, and backing sales tax out of that budget gives the shelf price you can actually afford — venue prices are usually quoted before tax.
Merch allowance
Merch budget = ticket price x share/100; ceiling per item = budget / (1 + tax/100) / items wanted
A quarter to a third of the ticket price is a common self-imposed cap. What matters more is deciding the per-item ceiling before you are standing at the stall.
Because stall prices are usually pre-tax, so a budget that ignores tax overshoots at the till. Working backwards gives a shelf-price ceiling you can compare directly.
Often yes on price, but shipping and the absence of tour-exclusive items cut the other way. Compare the online price against the ceiling shown here.