Shopping with Dad

Dad likes to shop. There are not many things he can do, but shopping is something he can. He can not see prices though. He cant read the small print.
He really likes to shop on Sunday after church. At Walmart. (Are you seeing where this is going?) In our town, we have two walmarts. One at the west end of town (nicer) and one at our end. Ours is a little cheaper but you must battle through the many many huge hispanic families to get down an aisle.
So here we are on a Sunday afternoon, at walmart with 20,000 of our closest neighbors...
I have things to buy as well. But dad walks in and goes trucking to the back because this is how he shops in this store. If you need to look at something, forget it, you just lost him. He is a slippery little sucker. Because he is old, because he is mostly blind, he barrels through entire families taking out small children on his way. This is the fun part of shopping with dad.
If you are not beside him, he will buy the $8 milk. He will buy the most expensive brand because it is easier. He won't ask. But if you point it out, he will switch. I would say just let him buy what he wants but he cant afford that.
I will try to buy his groceries to help him out. My thinking: if I buy his groceries, his bill will be lower at the end of the month. His thinking: now I can buy more things I don't need.
If by chance I do lose him (happens every time). I will spend the next twenty minutes trying to find him, bear in mind, he can't see me until I am sitting in his cart. He will continue his shopping, check out and wait outside. WTF???
If he continues his shopping on his own, there will be things he cant see so he wont get them. So about half way home he will say "I couldnt find the wax paper and I need it today". Hhmmm wouldnt it make sense to stick with the eyes and get your stuff the first time?