If you are going to try and get ticket+coach package then as @gooner1990 says, Bristol, Bath and Taunton are the closest pick up points for Glastonbury, however demand for these tickets will be extremely high due to their very closeness.
The problem with coach+tickets packages is that they amount to less than 20% of the total number of the public tickets available for Glasto and these are spread across 42 departure points. This means that some towns/cities could have as low as 50-60 ticket+coach packages available.