I got the S bag on the front and a carradice saddle bag on the back. It works nicely for me, the saddle bag can stay on and doesn't affect the fold. However if I was commuting and had to store the bike in a really tight spot on a train I think the carradice would get in the way, and it is too fiddly to take off and put on easily. I would try some of the other options suggested here.

Let us know what you decide. The S-type is a lovely bike, I have been through quite a few folders and it is the best so far.