If you want to do any tours, pay the extra $30 or whatever for the "luxury" options. Instead of being crammed on a bus or crappy uncomfortable van for hours with crappy A/C, stopping at mass market feeding, and moving as a mass of humanity through whatever you are visiting, you pretty much get the opposite. Super comfy recliner SUV seating, cold drinks, casual pace...
If you can swing it, a boat cruise around Ha Long Bay is absolutely worth doing. But get the two night package. The one night is so much time in transit you are basically on and off the boat. You get way better value at 2 nights.
From Hanoi the Hoa Lu and Tam Coc tour is a good one too.
In Hanoi don't miss the Thang Long Water Puppet Theatre. Bonkers fun. You won't understand a word, but the action speaks for itself. Be prepared to wait in a bit of a line, though.
Try to find somewhere that does a Pho Cocktail, it's incredible. A drink that tastes like the soup, and is made like this:
We stumbled across it here:
https://maps.app.goo.gl/eMRfERfk6rtQBdDa8