How to use the items I buy with satisfaction points??

If you purchased the Forever Full trait for 10,000 points, your sim won't ever need to eat. It is automatic, you don't need to use anything for the bonus to work. However, If you still see that the hunger bar going down, then it could be cc you have downloaded. If you do have cc downloaded. With the recent game update, it can be broken. To test it, disable the mods in the settings, restart game, and see if the bar is still going down. If it is then it's likely that it is a game bug but, I don't have this problem on any of my save. There is also a hardly hungry trait for 4,000 reward points. If Hardly Hungry is the trait you purchased with points, it makes sims' hunger need decay at half the normal rate the bar will still get to red and your sim can still die if you don't feed them, you just have to wait for this longer. You don't need to use anything to start this bonus, it is automatic.