The best accessory I bought was the extension table for the left side of the machine. Yes, I know lots of people use a card table or ironing board but the extension table attaches firmly and doesn't move; I had trouble with a card table moving out of position. It gives you a lot of extra room and prevents pulling or tugging of the quilt. I feel the expense of the table was minimal.
I haven't used any rulers, have you? I'm interested to hear how you like them.