We recently took a break to Sussex and went one day to do the Winnie the Pooh Walk From Gills Lap. The map on the PDF showing the route to the starting car park was tricky to divy-up with a larger map. This is the grid location for the car park where the route begins:

Google maps Gills Lap link (51.064353, 0.092989)

We also struggled for some time to find the bridge where Pooh Sticks were first played. Follow directions to this car park:

Google maps "Pooh" car park link (51.078726, 0.099677)

Follow the downhill path to the bridge. Note you first pass a smaller bridge and then come to the proper one after another 3-4 minutes of walking from the first. Walk 25m further from the Bridge and you find a tree stump with a door in the side.