I am going to try this in December. I have read about it and thought about it and wanted to do it, but I've never gotten the nerve. Finally, after doing the math over what I could save if I could just get everything I need from Sam's (mostly) for one month. And that includes about $20 in gas for a round trip - $10 if I have a partner in crime for the trip.
Step 1 - know your prices: my mom wanted to go to Sam's one day last week when I spent the week with her, so I made notes of prices of things I buy so I could do the math
Step 2 - meal plan: in order for this to work, you have to have your meals planned in order to make sure you get enough in your trip that you not running out to the grocery store all the time during the month
Step 3 - write out your list: base this on your meal plan, AND add a few convenience items or extra lunch items just so you don't run out
Step 4 - set a date: pick a day and hopefully pick a 'date' and take someone along that's not a kid
Step 5 - leave your kids at home: little ones make you rush and make poor decisions, plus they don't want to be there anyway
Step 6 - cargo space: make sure the vehicle you take can fit plenty of stuff, and that it's free of clutter which can take up precious cargo space (especially if 2 or 3 of you are going)
Step 7 - cold storage: coolers and ice for refrigerated and frozen items
Step 8 - plan a snack or lunch: picnics are still fun unless it's cold, then you may want to take this opportunity to go out to lunch with your girlfriends
Step 9 - fill your tank: if you start out your voyage with a full tank, then upon return, you can refill it and you'll know exactly how much gas money to collect from everyone
Step 10 - have fun with it: saving money is serious business, but don't let it be a downer - take some friends, have some friendly conversation, and just enjoy each other's company while you ride. You may also learn some secrets to saving money here and there from your friends.