1st off....What kind of geese?....What time of year?....What part of the country....What guide service?
K.I.S.S....On the chokes and ammo....Depending on your shotgun (assuming it's an auto loader)....Plain MODIFIED equals steel FULL....I like Kent Fasteel....3 1/2", 1 3/8 oz., 1550 fps, and depending what kind of goose (snows, specks, honkers)....1's, BB's, or BBB's...If in doubt, I always go to the BBB's....Guides want you to have some shooting....So, many of your shots will be farther than you think, especially your 2nd and 3rd shots...In a 3" shell, I would select the Kent Fasteel, 1 1/8 oz, BB's....If you can afford Bismuth or other high end alternatives, do so...My experience has been, they don't kill 'em any deader....You're allowed 11 lbs of shells, if you're flying...Works out to about 4 boxes....Ask your outfitter what brand and what shells they're using....
Etiquette wise....Always offer to help set-up and pick-up (it really does make it more fun)....The guide will normally be the one to call the shot (Take 'em)....Don't be the guy that tries to get the 1st shot by shooting early....You'll have other shooters with you....If the birds come in on your left and you're on the right, the guys on the left shoot 1st....Don't swing or shoot over someone's head....Don't be a "My Duck"....One bird falls out of a flock and one guy yells "I got one" after 6 guns have shot....
Good luck and have fun....
ps....Don't forget to tip the guides............