Bring a water bottle, a waterproof camera, possibly waterproof clothes (though you will be warned when your in the “splash zone” during shows) and possibly your own food.

I used to have a membership to the Aquarium (unlimited access) and it pays for itself after just a few visits. It’s a wonderful place to visit, rain or shine (many exhibits are indoors) but the food is expensive. The Aquarium is a research facility, though, so it’s not like your money is going nowhere; there are usually animals in the process of being rehabilitated (see otters rescued from oil spills for example) and marine behavior is also studied, so it’s very worthwhile.

Spend a weekend in Stanley Park, and make sure one whole day is spent in the Aquarium.