Some stores have just given me a price-adjustment with just the receipt.
I try to plan my purchases for the last valid day of flyer. Often, you can see a preview of the next week's flyer online. So, you can have a peek into most offers for the upcoming week before deciding to buy or not. Not all stores offer sneak preview peaks of their flyers one day before the flyer is 'activated' or valid, but I find that most of the major chains do so.
Also, some flyers activate on different days. For example, Safeway/Walmart/Coop/SavOn Foods flyers start on Thursday, but No Frills and RCSS do not start until Friday. The one day overlap grants me an extra day to look at the flyers before deciding if I need to make the purchase at NoFrills or RCSS.

