stuff u can waste IP on, that could possible be of some benefit now or in the long run:
new Champs: Of course, if u play more then a few games a day, you'll have well enough IP by the time a new champ comes out, as the gap is ever increasing it feels.
Rune pages: If you don't have max number, get them, make pages for your top champs, or gag pages for Aram/Bots to just have fun with. Like pure mana when playin Ryze/blitz/kass. or Pure crit for GP/Yasuo.
Runes: get every rune. Riot does change the effectiveness of different runes once in a blue moon. Never know when runes can become good. Also see my Rune page answer.
Summoner Name change: Have a flavor of the month name. When u main a different champ, change ur name to match it.
Riot will never make Skins available for IP. They are one of the main sources of income for them on this true Free to Play game. everything needed to play this game is available via IP, which is free (all be it time consuming). Skins are non-gameplay affecting things. Same with summoner icons, and Ward skins.
If your IP is upsetting you because you have too much of it, maybe you're playing this game too much.