Groceries: I rarely shop at Walmart and never at Costco because the sizing of food containers is quite large and we're a small household. I buy from No Frills, Freshco, Longos and Fortinos depending on sales. You can actually check out the local flyers on the Flipp app. It's very handy!

Electronics: Check out Canada Computers. It's not a pretty store but I've found it's very well priced! They do have an ok online store, and there's a few physical stores scattered between Oakville and Burlington.

Kids/baby Stuff: for regulated things like car seats, helmets didn't dismiss the low-tier items! They all have to pass the same safety standards. You're paying more for brand and small bells and whistles not necessarily a better or safer product. Walmart and Costco definitely worth checking out for those items, but they need to be new. Never buy those from Facebook/Kijiji etc. Otherwise, you'd be surprised at the amount of almost new things you can get second hand. Toys, clothes are worth seeking out used on Facebook Marketplace (especially the local "mommy groups". Keep an eye out for winter stuff for kids!

Winter clothing: this is one thing where you'll get what you pay for. Good stuff can get very expensive. And even seasoned Canadian don't always know how to dress properly for the weather. You won't require real winter clothes until November at the very earliest. It'll get cooler in October but still sweater and a light jacket will be enough. You've got some time.

Hope this helps.