derrickgoh is pretty much spot on.
I'll also suggest 2 sets. With the 3 sets they will issue you, you should have 5 sets that will last you the rest of your cycles (unless they don't fit again lah... lol). 6 sets is a bit overkill.
Try to get your stuff before going for ICT. While it is true you have a lot of time to go to your camp emart to shop, 99.9% of your unit mates will have the same idea. First day emart is always super packed. Second day emart is empty, no people & no stock of everything also.
If your backpack is cui, buy the new one. Not very ex and you will need it anyway when you have mob later on.
No helmet, then just get ready to sign 1206. Cannot buy from emart. Think it's about 200+. If you have friends who MR, get from them, and bring back to camp, and tell your PC that helmet cannot fit, need exchange.
Finally, it's possible to get your uniform during the same ICT. My last ICT (dec 11) was LK, 5 days. Monday am e-sizing, friday am issue new uniforms. Friday pm all change into new uniform and go for CO COC parade.

