Is it possible to buy stuff on amazon or online retail stores ( walmart, target, etc,) without a credit or debit card?

You might be able to buy it using Paypal or you can do what I do. If you are a member of the the local Secu you can buy pre-paid credit cards for $1

You may be able to get walmart to deliver to your local shop and pay cash on collection. I know a lot of UK stores do this.

How much spending power will I get for a dollar??

1 pound = 1.63 dollars

I heard you can buy amazon gift cards, redeem them at their website, and buy stuff with them.

is it true?

It is like a gift card, but you have to pay the card holder a fee. So I payed $1 and then $50, then I got a card with $50 on it :)

yes, a lot of big stores have them. Check out your local Walmart 

thanks a lot dewd.

In the future you will probably get a lot better and more responses if you actually put the question in your thread title.