At some point you may need stuff that isn't stocked in even the largest convenience store within the old city. This is when you need to turn to a shopping plaza. Here they are from the oldest to the newest.
Central Kad Suan Kaew
This is just outside the northwest corner of the old city and can be reached on foot, but you will have find convenient crossings for the moat and the busy inner and outer ring roads, never easy.
This shopping centre is a bit long in the tooth and has empty shop spaces, but it does have a good supermarket and decent food court. This is where I ate the pastries mentioned in another post.
Central Airport Plaza
This is newer than Kad Suan Kaew. It has nothing to do with the airport except that it is in the vicinity. Some shoppers make this the last stop before leaving on a flight and indeed the free shuttle goes that way returning from the plaza. The bus drop off and pickup is accessed via the Northern Village section which has handicraft stalls and is above a food court. Shuttle pickup is from several hotels around Chiang Mai, but you will have to sit in a songthaew for up to an hour while the shuttle does the round. So you may prefer to catch a taxi or Grabcar there and take the shuttle back. It's easy to find the schedule and pickup points online.
Central Festival Plaza
This one is on the outskirts of town and is newer again. You can reach it by shuttle van though the route is even longer. Another drawback is that they don't run all that often. I took a Grabcar there for just under 100B.
It has many well-known anchor tenants as you can see.
Decor is modern.
For some reason Japanese restaurants dominate the eateries. Perhaps it reflects the expatriate population or the tourists. I daresay there will be more Chinese restaurants in future.
More of that curvy architecture.
Schedules are hard to discover on the Internet. I did find one recent post with pictures of the schedules which turned out to be up to date. As a public service, I have scanned the paper version I picked up (Feb 2019) and post them here. Click on the images for the full size versions.
The departure point is a short walk from the doors with the schedules. Although the schedule says for hotel guests only, nobody is going to bar you from boarding or disembarking even if you are not. I took the shuttle back to Hotel M.
There is another shopping mall to the north-west, further out of the old city, near the highways, called Maya Lifestyle Centre. I didn't visit this. Reports say that it's full of upmarket boutique shops, but does have a good supermarket.