sending envelopes to America

I am sending some post cards back to America with a pack of gum and some candy in the envelope. The envelope is small like a post card. Is it ok to have these items in an envelope, or is the post office going to want me to buy a box to put them in. I have never sent anything to America before, so I am not sure what their requirements are. Also, what is the cheapest way to send something?

From Japan to the USA?

I would recommend a bubble sheet-lined envelope (look in at a stationery shop) bigger than the postcards, so that the bit bulky candies would fit in comfortably together, and so that the envelope would not burst/get torn by accident.

Just take the parcel to the post office, and they can tell you the air mail (7 - 10 days or so from Japan to the US) and surface mail (not recommended; takes two months) postage. Surface mail is cheaper, but you would not really want any candy to stay on the ship for two months or so and risk melting/going bad, right?

They might ask you to fill out a small customs declaration form - you just write out on the form what it is, mark it "gift," put a small amount (I imagine so for a pack of gum or so).