Słubice
Słubice is a little town at the German/Polish border. If you get dropped in Frankfurt (Oder), it might make sense to walk here (just over the bridge) to hitchhike into Poland.
Hitchhiking out
East toward Poznan, Warsaw E 30 2, southeast toward Wrocław 29
Walk along the dike until the end of town. This road, national road 29, is the only route leaving the town to the south and goes straight to Wrocław. Several kilometers outside the city, there is an intersection with the E30/N2 which go east to Poznan and Warsaw.
West towards Germany
Instead of hitchhiking from Słubice, you can walk over the bridge to Frankfurt (Oder) and take a bus or tram to the German motorway.
It is also possible to go to the parking place of the cigarette shop in ulica Kościuszki. You find it close to the roundabout opposite the Collegium Polonicum behind the shopping centre. A lot of Germans from Berlin and other places come here to buy cigarettes. You can ask them to get a lift, look out for their licences plates and if you approach them before they enter the shop you can point out that with one more person in their car they are allowed to legally import one(?) extra carton of cigarettes.