Any suggestions of in-game purchases for my Sonic Line Runner game?

Hello, I was creating a Line Runner game which you can see here
I would like your opinions on what are the best in-game purchases for a Line Runner game where you can not only jump with [SPACE] but also strafe to the left and to the right with [Q] and [D].
It is a infinite level in 3D (sort of) where you must jump the obstacles and avoid them by going to left or right. There are sometimes rings that you can collect to boost your score. Score has no utility yet, only to be showen to the Leaderboard.
There is also a character customization menu, a little simple but it works.