Just to be perfectly clear here for those who are reading. As well as "jacket and tie", make sure you have dress shoes. You'll read on the sites web pages "no trainers" -- for North Americans that translates into "no sneakers".
And yes, the lunch is definitely not to be missed.
Two things got me at Muirfield:
1) Cut doglegs at your peril. The long grass can kill!
2) Yardages are to the front of the green, including the yardages on the par 3s. For some reason, figuring the numbers on the par 4s and 5s weren't a problem for me, but the par 3s were. I'm used to getting to a par 3 tee and having a sign say 156, then not having to adjust it too much. At Muirfield, if the pole says 156, you'll never use that distance, middle of the green will be 170 or so.