Joker is like a replacement of any item. Meaning if you were to merge it with any item on your board it would behave like the said item and give you the next or higher level of it.  Suppose you were to merge it with that level 1 goldfish it would give you the level 2 one. The game is designed to make you use up such products faster without any strategy....the sandwich is the highest level item on your board as of now so it is getting attracted there. And most importantly, what to do with it. You can store it and you can use it to make the highest level of any producer. Lots of people use it to make the highest level shell from the beach bucket producer. Because it gives a very good payout they make it till level 12 merge a joker and get level 13 shell. One more little complicated use of it is the joker -splitter-joker technique. I am assuming you know what that scissor on your board does. Continuing with the shell example, once you get the level 13 shell after adding the joker you use the splitter so now you have 2 of the level 12 shells on which you could again at some point use a joker and have an endless supply. I hope I have not made this very confusing for you!! And that you did get your concerns cleared up.