The only thing I've come up with so far (just an algorithm, not any kind of formula because I don't know what I'd use):

I have my 50-52 columns for the weeks of the year, and then at the end I have a column for formulas. A cell in this column would count how many cells to the left it has to go before it hits a number (either a number that's not a zero or any number at all - I probably won't be putting zeroes for every single person who doesn't bring a guest).

This way, I could use those values to create a new sorted list of members.

So I supposed I'd need two things: 1) a formula that counts how many cells to the left it takes before a number is found (and report back how many), and 2) how I create a sort based on those values.

I suppose I could just have a second sheet that showed the members and their values, then sort it manually, but where's the fun in that? I just don't know if there's any way to automatically sort a list or populate a list in a sorted order...