It ultimately depends on what you need to do. If you don't need hardware
acceleration for graphics (which 3-D games, modern desktop environments, and
tools related to working with 3-D will run more slowly without), most of them
will basically work. However, it's highly unlikely that WiFi will work,
certain if I'm not mistaken that Bluetooth will not work, and possible that
graphical hardware acceleration will not work.
First thing's first: all of the stuff sold by Think Penguin and Tehnoetic
will work perfectly with Trisquel:
http://libre.thinkpenguin.com
https://tehnoetic.com/
If the laptops sold by Think Penguin are too expensive, you'll have to go to
one of the more mainstream stores, and that's where it gets tricky.
For graphical hardware acceleration on laptops, your only chance of getting
something that works is to get an Intel CPU. Until the Skylake and Broxten
CPUs, whose integrated graphics have started requiring proprietary firmware
blobs for hardware acceleration, all Intel integrated GPUs were powered by
completely libre software drivers.
For WiFi and Bluetooth, you can get the mini adapters sold by the stores I
mentioned above. Depending on your needs and laptop, you may alternatively be
able to just use the Ethernet port for Internet access. (Some Ethernet cards
require proprietary firmware blobs as well, but I don't think they're as
frequent as wireless devices with this requirement.)
