First week on the envelope system of budgeting

Yesterday, Cliff's payday, I got enough cash to put some in the following envelopes:  groceries, dog, clothing, doctors-and-pills, and fun.  Hey, they're my envelopes, I'll name them as I please.  
I'll be fine-tuning this thing for awhile; I've designated $75 weekly for groceries, and I really don't think we'll be spending that much.  Yesterday I got by for under $50.  The only thing  that has made my grocery bill seem high in the past is that when we shop at Walmart, we're liable to be buying $20 worth of oil, a $30 pair of overalls, and so on.  For now, Cliff will buy oil out of his pocket money (he gets a pretty healthy allowance), and overalls will come out of the money in the clothing envelope.  I do count toilet paper and paper towels as grocery items.  Which reminds me, when did paper towels start costing $2 a roll?  I think I'll be using my micro-fiber cloths more, in the future.
The system sounds so simple.  And I will tell you that it made me quite conscious of what I was buying yesterday, which always means I spend less.  
I've allotted $20 a week for the dog, which sounds like a lot.  But there's her pricey dog food and those expensive heartworm pills and the monthly flea stuff.  Plus the fact that if we leave for more than one day, we get her boarded to the tune of $15 a day.  Now that I think about it, I may have to allow more for the dog!  Good grief, is it possible a dog can cost $80 a month?  
But that's what I like about this system; it makes you realize where your money is going. 
I had my first rude awakening yesterday when I stopped to pick up a couple of prescriptions I hadn't planned on.  My generic blood pressure tables are only $10 for a ninety-day supply, but Cliff's Niaspan is  $90.  Yes, friends, a dollar a day.  
Since I just started this envelope thing, I had set aside $35 for meds.  But my first $35 just covered Cliff's deductible at the cardiologist's office, leaving me with an empty envelope.   So, how would I pay for the prescriptions?  
Luckily, Cliff is still working, so we have the money.  And some extra money came in this morning, so I was able to put the allotted amounts in each envelope.  
It's a good thing I'm getting this going before he retires.  It's going to take a year just to get ahead of things.