I actually drink a can of SlimFast for breakfast and lunch Monday-Friday. One can only supplies 190 calories, which isn't much, especially if you are doing any sort of labor. On the other hand one can supplies about 1/3 of your daily vitamins and minerals. They have about a one-year storage life. From the back of the can:
serving - 1 can/325 mL
calories - 190
fat calories - 50
total fat - 6g (9% rda)
saturated fat - 2.5g (13% RDA)
trans fat - Og
polyunsaturated fat - 0.5g
monunsaturated fat - 3g
cholesterol - 5mg (2% rda)
sodium - 200mg (8% rda)
potassium - 600mg (17% rda)
total carbohydrates - 24g (8%)
dietary fiber - 5g (20%)
sugars - 18g
protein - 10g (20%)
Vit. A - 32%
calcium - 50%
Vit. D - 35%
Riboflavin - 35%
vit. B6 - 35%
Vit. B12 - 35%
pantothenic acid - 35%
iodine - 35%
zinc - 15%
manganese - 35%
molybdenum - 30%
vit. C - 100%
iron - 15%
vit. E - 100%
thiamin - 35%
niacin - 35%
folate - 30%
biotin - 35%
phosphorus - 50%
magnesium - 35%
selenium - 25%
chromium - 35%
rda's based on 2000 calorie diet.
experiation date Nov 2008 (purchased January 2008)

Overall, you are probably better off storing "Ensure" rather than SlimFast so that you get the calories you'll need. I think both are available in powdered form which could store easier but does require water. Another option is SlimFast plus sugar.

A case in the closet for short term emergencies might be okay but overall though I think they are low on the list of long-term survival foods.

-Blast

p.s. Oh hey, welcome to the fire newguy RzrSxS!