Believe it or not, there is a
hardware store. This is a godsend to cruisers, though if you are chartering not so much.
I'd rate it as "rustic" and "austere" but these terms depend upon your perspective. There is no Costco, no Walmart. Most goods are not only made in
China, but it's the junk
China makes for 3rd world export. But again, you probably don't care about that.
The open air market is very inexpensive, fresh fruits, fresh
fish, etc. But it's not open every day. Ask the charter company when it will be open.
And there is a market, so you can certainly find enough to satisfy minimum needs.
Oh, warning: they aren't oranges, they are bush limes- orange limes that look like oranges. They will give you a pucker.
The best thing you will see is the Tongan people. They are wonderful, particularly those from Vava'u. Try to learn basic Tongan before you go, it will get you far.
If you overnight/day on Tongatapu be aware that the country (the entire country) is closed on Sunday. There is a lua'u in a cave, run by a
family, I forgot the name I'm sure it's on the internet- absolutely great way to segue into Tongan
food, song, and hospitality. You can skip the museums and cultural center. The Billfish is the old-school pub with lots of
history. And see Ha'Amonga the triathalon. Don't eat at raw fish at the market by the wharf, a bunch of us both palagis and polynesians got seafood poisoning there (more than once).