services on the M5 are at Frankley (near Halesowen) and Strensham (Junction 8, M50). Both are accessible north and south. There are no services at Droitwich.
There are no services at the Droitwich junction (J5), but if you take the exit for the A38 towards Bromsgrove, there is a big McDonalds and a Travel Inn type hotel 50yds on your left. This used to be the site of a brilliant 'greasy spoon' transport cafe, but it was denolished about 10 years ago, mores the pity!
Oh, and be aware that the North and South Strensham services mentioned by mushroom are about 2 miles apart, so you can't 'walk over the bridge' from one to the other.