What you have in the first picture is a knurled-headed thunbscrew. These would work fine, but a spade headed thumbscrew is a bit less expensive, and since it has a wider head it would allow you to exert a bit more torque for tightening or untightening.

Check McMaster-Carr at www.mcmaster.com, and search for "thumb screw stainless". You'll see a listing for the spade headed type, as well as the knurled headed type. Notice that of the spade headed types, one has a shoulder and one does not. Try to get the shoulder types. That shoulder rides nicely against a washer to make tightening these things very easy.

If you should buy the type which does not have a shoulder (in my area these are all that I can easily find), you can improvise by threading an ordinary nut up to where it hits the spade head and can't go any further, thus giving you a "shoulder"

If you are into doing a bit of soldering, you can make make a very nice substitute for a thumbscrew by soldering a washer into the slot on the top of a slotted round-head machine bolt. The hole in the washer allows you to insert a string (or a safety wire) which can serve to keep the bolt handy, whether it is installed, or removed.

The tee nuts ('T" nuts) in your second picture are probably the higher priced variety as well. Those you illustrate, though, probably would not be suitable, as they don't seem to have much ability to grip the wood. The usually chosen "T" nut has long teeth that really bite, and probably the most commonly used is the 1/4 x 20 size.

The photo at the bottom comes from this web page:
http://www.tperformance.com/street_rod_store/hardware/

Another option is shown on the following webpage, and called "propeller nuts".

http://www.hardwareselect.com/k9.htm

And then there are similar items known as threaded inserts. These are available in brass, and zinc, as well as stainless steel.

"T" nuts are installed from the back and are the least expensive. Threaded inserts are usually installed from the front, and cost a little bit more.

Hope this helps

PGJ