The issue boots are now decent - Meindl - (although you might want to get yourself a pair of better insoles) - admittedly I prefer the old-style Lowas I bought about 3 years ago when they were issuing Desert Magnums. The issued ballistic glasses and goggles are free and no worse than the $100+ ones at the PX.
The issue glasses are actually on sale in the PX, at around $50-60
I would say the only thing I class as an essential (if taking ipod mp3 etc) is a powermonkey explorer Linky
add it to basket, then enter 'TROOPS' in the voucher code bit, and watch the price drop by almost 50%
i was on my first tour last summer and had the same sort of worry
you'll get everything you need and more, all the extra bits are things like mp3 player, psp or the like... just stuff to fill your free time. and bring cards... sounds a bit lame but poker is defo the way to pass the time