Does not valid with any other offer include items on sale?

Answer 1

The phrase usually appears on coupons, and typically means you can't combine such coupons.

You may or may not be able to use it for items that are already on sale ... technically, the coupon says you can't, but sometimes the store will go ahead and let you do it anyway.

Also, at most stores you can purchase an item on sale and use the coupon on a different item. Again, technically the language on the coupon disallows this, but most of the time the store doesn't really care much... the language is mostly to keep some smart aleck from coming in with ten 10% off coupons and claiming that he should get the item for free.