Love the Wicked Oyster. We generally get there 10-12 times a summer. One of our favorite Cape restaurants along with the Impudent Oyster in Chatham. (Probably a bit too far out of the way if you’re staying in Truro.)
You could hit Truro Vineyard. Is is the best vineyard in the world? Nope. Are you going to leave with two cases of wine? Nope. Is it a fun way to spend part of an afternoon. Yup. You can also visit their distillery, South Hollow Spirits. It’s basically on the same property. Tastings for both are not expensive.
The Atlantic Spice Company is fun place - bulk spices, teas, etc. If either of you like to cook or even if you don’t (we don’t), it’s kinda cool.
If this is something you want to do to kill time, just call the places in advance...they’re all open today, but offseason hours on the Cape can be set in sand.