There are sponsorships and TV rights in the game... And you can earn cash or tokens.
I think it will be more interesting and realictic if there will be some contracts with the manufacturers of equipment (like adidas, nike & etc. in real life). So you will be able to choose one of them at the begining of new season (depends of the results of last season).
Each manufacturer has its own requirements for the contract signing (like place in the league or some % of victories through the season). And each manufacturer give its own improvements to the team.


Some examples:

Shirts:
1) Manufacturer #1 -> need to be at least 4th in the end of season -> Gives +3 to Fitness of every player in team until the end of next season.
2) Manufacturer #2 -> need to be at least 7th in the end of season -> Gives +2 to Fitness of every player in team until the end of next season.
3) Manufacturer #3 -> need to be at least 10th in the end of season -> Gives +1 to Fitness of every player in team until the end of next season.
Boots:
1) Manufacturer #1 -> need to be at least 3th in the end of season -> Gives +2 to Speed and +1 to Dribbling of every player in team until the end of next season.
2) Manufacturer #2 -> need to be at least 3th in the end of season -> Gives +1 to Speed and +2 to Dribbling of every player in team until the end of next season.
3) Manufacturer #3 -> need to be at least 6th in the end of season -> Gives +1 to Speed and +1 to Dribbling of every player in team until the end of next season.
3) Manufacturer #3 -> need to be at least 10th in the end of season -> Gives +1 to Speed of every player in team until the end of next season.

And if you (developers) want you can add some real manufacturers (like adidas, nike and etc.), call them "official"/"premium" manufacturers and sell their season contracts in Club shop (like "official" logos and jerseys).


P.S.: sorry if there are any mistakes, English is not my native.