Do something new!
Game jams are awesome for doing new things, especially since you have a deadline it motivates you and you don't work weeks on something that MIGHT not be good. Make sure you learn at least a few things from it and it definitely wll have been worth it!
DO NOT make an inventory system... DONT!!
Keep it a bit small, work on one or two mechanics. Sometimes less is more, this ALWAYS counts for game jams.... ALWAYS
Anyways overall just have fun, try to learn some things and do something new! If your game isn't great upload it anyway! Might just get some constructive feedback! Most people in the gamedev community are very nice!