True true, but Costco is more efficient as there is tons of food (and space, if you have a forklift and the time to operate it) and is a more defensible location as it is purely surrounded by walls. There may also be vehicles and such in the back (think 18-wheelers) which would be used as moving barriers and/or zombie charging weapons.
I'm not saying a Military base isn't a good idea, I'm just saying there's a 20/40/40 of it being completely overrun with zombies, the military still residing there, and it being abandoned (in respective order). Costco is just more of a viable solution as there's only a 50/50 chance of it being overrun or a safehaven waiting to happen.
All depends on what it's stocked with. If you're simply looking for space to operate out of, a warehouse would be a good idea as well as a cubicle storage facility (Typically each cubicle section can have a large sturdy metal door closed down to shut it off, helping stave off a section in the event of an overrun). If the warehouse is packed with useless stuff like, eh let's say, spark plugs and monitor cables, I'd choose the storage facility over the warehouse (If the SF wasn't overrun, of course). But if the Warehouse was empty or stocked with useful stuff, I'd be more likely to take it.
In the end if you're looking for quick access to guns and melee weaponry, a gun store is a better choice than sticking your neck out for bad chances at a military base. Not to mention if you find welding equipment and a power source, you can weld things to vehicles and create a viable transport solution (Charging through hordes). Really, it's all how you want to handle a zombie situation. I find normally that civilian places are an easier target mainly because hey, what if the military was the virus's first target (We're talking bio-weaponry zombie viruses from terrorists or other countries here, meaning the virus is targeted at certain countries/points) and it turns out that the military base is a huge fuck up as the zombies there are ridiculously over-powered?
Acttualy, sorry to say this, but you guys would be the first peple to die in a zombie apocalypse.
When the zombie come, the places you guys listed would be the first places anyone would go to. That mean's people will kill eachother for the recourses avaiable (this is by no mean's farfetch'd. We've seen that happen multiple time in history, during times like war). Also, a big number of people in an area will increse the chance of one of them being infected, and if there is one zombie in a crowd, everyone's fu*ked,