If you cross to the West Bank, you can head West to Merrit or South to Penticton, Osoyoos, and the Okanagan. North out of Kelowna lies Salmon Arm, Vernon, Kamloops. East lies Highway 33 which heads into the Kootenays and can be a lonely road.
South/West towards Vancouver
To hitch to Vancouver from Kelowna, take a city bus to the Westbank neighborhood, and wait on Main Street, as far west as one can walk before the road becomes an expressway. A sign will help clarify your direction, as many cars are headed south. If possible, try to get to the junction of the 97/97C, and wait just past the dirt road with the cattle guard. At this point, traffic is splitting between those heading west or south, and there is lots of room for people to see you and pull over (the walk is about 1h long).
East towards Grand Forks
More research is required but if you head out of south-east Kelowna on Highway 33 you can reach Rock Creek, which can go to Osoyoos or Grand Forks.
South towards Penticton
Rides along Lake Okanagan are super easy to get. The route is Highway 97 out of West Kelowna. Public transit or thumbing can get you out of the city, and then its just a matter of personal preferance as to where to start thumbing. You can also hit the Okanagan Connector to Merrit on Highway 97c. From Penticton, there are several routes to various points.
(Option 2: Bus system) Take a 70 bus to Penticton from the Queensway Exchange downtown Kelowna. They leave at 7:40 AM and 5:10 PM.
North towards Kamloops
Highway 97 North out of Kelowna will take you through Vernon, and on to Kamloops. You can also take the same route towards Vancouver and get off in Merrit, then head North.
It is reccomended that you ask to be dropped in Kelowna proper as it has more to do and see than WestBank but be aware that its a long haul back to the highway if you intend to continue south or west.
Places to avoid
Accommodation and Sleep
Camping on the lake might be possible, there are lots of trails. A food truck does random stops near the waterfront in the evenings, good for a soup and sandwhich.
Other useful info
Lake Okanagan is refreshing but beware of sea monsters. There are fire spinners who jam on the beach, good people to hang out with.