Selling for Riot Points:
- Summoner's Rift skins
- ARAM skins
- Champion Splash Art Wallpapers (real life wallpaper not your computer desktop screen)
- Custom In-Game announcers
- Minion skins
Those are just off the top of my head. I'm sure the league community has tons of ideas for digital and real life items that Riot could offer for money or Riot Points that people would actually want and pay for, yet Riot takes the mobile game microtransaction route with their Prestige Skins which are worse than the base skins, and Eternal which is just a stat tracker that they already had years ago but decided that people should pay for that now for each champion.
I get that Tencent is tightening the leash around Riot's neck because they ain't makin' enough money and wasting a lot of it on Esports, but like any company, the problem starts at the top. The higher ups got lucky that this game blew up and didn't know how to properly make it a bigger success than it already is; and are copying other game companies' plans to make more money than they already are, but way worse because they didn't pay attention to their playerbase.