Giving God our junk and our leftovers

2 Sam 24:24-25

24 And the king said unto Araunah, Nay; but I will verily buy it of thee at a price. Neither will I offer burnt-offerings unto Jehovah my God which cost me nothing. So David bought the threshing-floor and the oxen for fifty shekels of silver.

25 And David built there an altar unto Jehovah, and offered burnt-offerings and peace-offerings. So Jehovah was entreated for the land, and the plague was stayed from Israel.