If you buy items one day and the next day they are on sale can you bring your receipt for credit if the sale is within a certain amount of days from date of purchase?

I believe so. Most places do that. Otherwise, you can return it and repurchase it (although that's a pain)

Yes return and rebuy

I really don't know sorry

Yes, sams can return and exchange for the lower price offered.

Yes

I would imagine that Sam's might, but I couldn't be entirely certain.