If you must have something sweet, check out the Healthy Choice and/or Weight Watchers ice cream bars. I've only tried the WW Giant Cookies & Cream bars, but they are yummy.
If set on getting diet drinks, yes the Kirkland brand is good. Better than Slim-Fast I think.
Today we just picked up some "Fulfill" -- along the lines of Propel I think. It comes in little packets that you add to a 16.9 oz bottle of water. Nice taste, change of pace from regular water. Lemon, Kiwi-Strawberry, and Wild Berry. I've tried the first 2 thus far, and the kids approve of the Wild Berry.
As for bottled water, big thumbs up to the Kirkland brand. Great tasting, inexpensive. Our tap water tastes funky, so bottled it is around here.