I just got out of RTC like 2 weeks ago.
They do not provide you with stamps. But you'll get to buy them at the nex before you'll even be allowed to mail letters.
You will be issued a NEX gift card for like $140. Don't buy a lot of stuff.
Everything besides your uniform items will have to fit in a very small drawer. So be conservative when you buy your living supplies.
You can also bring your own. Just keep them in your wallet. And I had my family send me stamps so I never actually had to buy any at the nex.
And the day you ship, dress as lightly as possible. You'll be sending all your clothes home and you'll pay by weight. If I could go back, I would have just worn gym shorts. No one got in trouble for what they wore into boot camp.
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