The Prestige System is an optional “no pay” system used by members of the government of the Yamatai Star Empire wherein workers are not paid regularly, but are provided for by the state and are able to request items they desire, based on their prestige.
You start with default standard issue equipment, which is pretty much your uniform and obligatory stuff. Starting soldiers in the Star Army of Yamatai have the benefit of being fairly well treated by the Empire's 'prestige system', which makes it so that any fundamental need they have (toothpaste, toothbrushes, hairbrush and other basics you might need) will be covered freely - that includes services such as food and living space rent (if applicable). Modest stuff, mostly… but it sure beats being broke.
You have 3000 KS, which is the currency you have over the prestige system to purchase privileges to improve your quality of life beyond your 'default' equipment. It's perfectly okay to hang on to those funds to use them later when you better define your character, or just go all out and take stuff that you think you'd want to have. It's best to keep in mind that your character was either serving, on the move between short assignments or studying… so, your possessions might reflect that.
A KS is roughly an equivalent to one US dollar. You don't really need to run prices past us for approval: just use your best judgement and whatever real life reference you might get your hand on.
Note: Ordering goods on the prestige system and then immediately selling them can cause a loss of prestige.