A point-of-sale setup for selling at shows — scan or log a card, take payment, and have it hit your inventory and P&L automatically instead of reconciling later from receipts.

Per-show P&L shows which shows are actually worth your table fee and travel time. Some shows sell volume at thin margin, others sell fewer cards at higher margin — you can't tell which is which from a combined total.

What you paid for the card, plus table fees or sourcing costs you allocate to it. Without this, your "profit" numbers are really just revenue.

Consigned cards aren't your inventory — track them separately so your P&L reflects only cards you actually own, not cards you're selling on someone else's behalf.