I think the only things I buy in them are branded goods, which are a lot cheapoer than the supermarket etc, for example, my local 99p store and pound land sometimes have King of Shaves, Gillette, and Bulldog shaving stuff, which is a good saving over other shops (and yes it is proper stuff, not with v similar name/packaging
)
I was buying batteries but found they don't work for very long in some items, or even at al, and have had a couple leak (I think there's another thread here about that or maybe on hukd)
brand name food there can be hit or miss, some of the energy drinks are 3 or 4 for a quid, which is good, but often when they have proper coke 4 cans for £1 it's v near its sell/use by date which makes you wonder how long ago it's been sitting in a warehouse before it was discovered!
also soem of the deals look better than they are, chewing gum multipacks, you get less packs, so it's no cheaper than supermarkets.