Karthus is a dead priest in some sort of dead church in some kind of necropolis...

Okay...

In response to the pool party ziggs splash...

LIFEGUARD RENEKTON

Ahri works at a convenience store and Veigar is her boss. Kennen, Akali, and Shen all work in medicine.

Zyra does gardening in her spare time, Lulu owns a semi-successful confectionary store across the street from Morgana's and have a big rivalry

Mundo owns Zaun and Noxus now and is a stock broker as well as a counterfeiter.

Yorick is a pool boy.

Renekton is a lifeguard.

Talon=Blade collector
Shaco=Joker/clown
Lee Sin=Martial arts teacher

Twisted fate is a cowboy
Taric owns a jewlery store
Twitch is a plumber
Tryndamere is a telemarketer
Teemo goes house to house selling mushrooms
Thresh sells bikes
Talon has a pet store
Tristana is a high jumper in the olympics

Ashe has set up a little archery range some near a small town in Northern Europe. It's a merger living but she enjoys the solitude

Soraka is a missionary, not for any particular religion, but just helping all she comes by.

Graves is still living a run and gun life. Gambling in Vegas, breaking in to fights with someone he has cheated, running form the law, the usual.

Heimerdinger and Corki, Piltover customs brought to life!
Time to bring the car in.

Ziggs would likely be the world's best chemistry teacher.