What do you give someone who always gives you money or a gift card?

My dad used to always just send me a check for Christmas. It left me in a quandary as to what to do in return for him. Should I use his money to buy him a gift. We were living on opposite coasts at the time, so I had no idea what he might need or want. Should I buy him a gift card with his money? Sure I could use money from my own bank account, but money is fungible. The ultimate inanity would be to send him a check in return. Should it be for more money than he sent me? Would that make him feel bad? How about sending less? How would that go down? If I sent the same amount he gave me, the reality would be nobody but the banks involved and the post office gained anything from the exchange.

How do you resolve distant giving to loved ones whose wants and needs are unknown to you?