The way I do it might not the way most people do the envelope system, but it works out awesome for us.
What I did first is that I went back through our checkbook, wrote down everything that we spend our money on, so that I wouldn't be forgetting something as I was making up the envelopes.
Then I went out and bought an accordian type binder that had the # of slots I was going to need to put the envelopes in.
Turned out I have about 20 envelopes that I fill each month.
Our categories (of course everyone's are different), are car insurance, house insurance, sewer, trash, license plates, doctor copays, prescriptions, nursing insurance, piano tuning, school pictures, psr, zoo membership, gymnastics, newspaper subscription, magazine subscriptions, girl scouts, home repairs, car repairs, christmas savings, and vacation/camping fund.
Most of these bill are either yearly, or every 3 months, so I divided it by 12 or 3 (whatever the case), and put that amount in each month.. so when the bill rolls around, the money is in there. For the categories such as home repairs, car repairs, prescriptions, doctor co-days, or christmas savings... I just made up a # of what I would like to always have in the envelopes and try to keep that in there.. so if I have to withdraw some, I replace it over the next month or 2 (depending on the amount I had to use up that month).
I also set up a natural gas envelope, because our bills vary so much from summer to winter.. so I added up 12 months worth of bills, divided it by 12 (which in our case equaled $120)... so in summer months, I add the difference between the bill and $120 to the envelope.. in the winter months, I take out what I need (over $120) to cover the bill... kind of my own "budget plan" instead of signing up for theirs.
I don't do envelopes for monthly bills... we get paid every other week.. we have 6 monthly bills (water, phone, gas, electricity, u-verse and visa). They're divided so that 3 get paid each time we get paid... then after those are paid, I go clean out our bank account of all the rest of the money... we fill all the envelopes... then all the leftover money is put into a single envelope that we live off of for the 2 weeks.. so when that money is gone, it's gone... luckily we've never run out yet.. think just the thought of paying cash for stuff has helped us back off a little in spending.