Day trip to Cannon Beach is great...though if you really want to do a loop I'd make the trek down to Tillamook and do the cheese factory, that is cool (that is if you like cheese).
As for Portland...
Powell's Book Store
Food
Literally, so many options of where to eat. IF you are staying on E Burnside, a favorite of ours is Ate Oh Ate, amazing Hawaiian food. Also in that vicinity, Screen Door (long lines), Paadee (great Thai food), Guero (just up on NE 28th, Tortas), Ken's Artisan Pizza (up on SE 28th).
Go walk SE Hawthorne up and down, between SE 39th and anywhere in the 20's.
Japanese Gardens
Oregon Zoo
Depending on the Weekend, check the Roseland, Aladdin Theater and other local venues to see if there are any cool shows to see.
Also, have to mention a drive up the gorge obviously, go see Multnomah Falls, drive up to Cascade Locks and hit the Eastwind Drive In for some awesome soft serve 🙂