If you are not claiming mileage then you are missing out on so much.
I have made a spreadsheet that I keep track of all my receipts in. I have it like this:
So under Grocery (50% deduction) I have headings as follows: Store, KM's driven, Amount. I just do a total at the bottom for km's and amount. I then have the other receipts for 100% daycare (groceries that I know were completely daycare, office supplies, crafts, toys). I do the same (store, km's driven, total of receipt, total deduction - I sometimes buy other things that are not 100% daycare so I separate totals here). I then total this section and give totals to my accountant.

If I go to 2 stores on one trip then so be it. I still claim full mileage for both but it usually doesn't happen often.