To stiffen the ends of the cord and to prevent fraying, I use clear fingernail polish. I paint some on, and gently twist the cord in the direction of the spiraled plies. After it dries, I snip the ends on a diagonal and paint a little more polish on. When making a large piece with a lot of small holed beads, I find I need to renew the ends from time to time. I find this most necessary with the Omega brand cord. As the C-lon is stiffer, the need is not so great. I've even made entire pieces with C-lon without the polish.
To secure end knots, I dab on some "Jewel Glue" by Delta. It is a fabric glue for attaching jewels, beads, & rhinestones to fabric. It is washable, so unlikely to dissolve if one of my pieces get wet. I don't recommend routinely getting the jewelry wet, but I may be overly cautious. I gave an ankle bracelet to a friend of mine about 3 years ago. She wears it all the time, and claims to even take a shower in it. It still looks much as it did when I made it. (Cord used was the Omega Brand.) I buy the glue at Walmart.
I use a variety of closures, but the most often: buttons, lobster claws, and toggles. I try to get silver or gold plated clasps. Hopefully, soon I'll be able to upgrade to sterling and gold filled. Still Fire Mountain Gems is the store of my choice.
With the buttons, some metal, most plastic; depends on the button. There is a lot of variety in buttons. I say, let yourself go wild! I get them at sewing shops, Walmart, etc. My favorite local supplier is Hancock Fabrics. They have a large selection, larger than they have in their online store.
Well, that pretty much sums up my materials. Thank you for reading this, hope you found it informative (and maybe a little interesting?). Feel free to leave comments, tips, etc.