I've written before about quality of your materials but wanted to go back to that.
When I colored my Prayer Rocks for the ladies church group, I realized that I shouldn't just use any colored pencil because the brightness of the color just wasn't there. I had to use my professional Prismacolor colored pencils and even though they're expensive, if you care for them (don't let them fall on the ground or the lead will break into little pieces inside!) they will last many years to come.
Some of my supplies I have had since art school which is fine as long as they aren't some paints that turn moldy. Inspect your supplies regularly and toss out the bad ones such as tubes leeching liquid or have burst open. Pencils, charcoals, and pastels won't spoil so they are fine to keep around until they get too small to hold...then you can buy a pencil holder. There are different kinds out there and it might change the feel of your grip but you'll get to the very end of your material.
My pastels are a set I bought while in Art School. So far I've never had to replace any of the chalks but am considering buying a new white piece in the next year. I have a white pastel pencil I'm using in the meantime, but the quality isn't as good as my stick pastel which brings out a great opaqueness and causes the highlight or pupil to just pop with a tiny dot!
Inks are another thing that you want to pay a bit more money to buy good quality. You don't want your art to fade so pay a bit more and save your hard work!
