Definitely walking around the canals and seeing the architecture. A fun place to duck into is the Mouse Mansion aka the Sam and Julia Shop (https://www.sam-julia.com). If you have (or expect) young kids in your life, pick up a book, as I found out the hard way you can't really get it here.
I disagree that a canal tour will put you to sleep. Certainly, one of the big boats probably would, but the smaller boats used by Those Dam Boat Guys (and, I assume, Captain Jack, who Forum folks also recommend), are livelier. I have taken two evening trips with TDBG and enjoyed seeing the buildings lit up and hearing how quiet the city is in the evening. If it's the last tour of the night and the captain offers to take you to the marina instead of returning to the pickup place, say yes. There is a very good local pub nearby that has delicious fried food, including bitterballen. (https://www.blaauwhooft.nl). I was there in March, but it appeared that there would be lovely outside seating in the summer. I really enjoyed the Texels skuumkoppe (beer), but they had a good selection of other drinks, as well.
You can bring your own food and drink along on your canal tour (with TDBG, anyway). I recommend picking up a prepared salad or something else that catches your eye at Sterk Staaltje (https://www.sterkstaaltje.com). For a sit-down dinner with Dutch (and French) dishes, try 't Zwaantje (https://www.zwaantje.net).