Always keep your dark clothes and light clothes separate. Washing lights with darks can make them dingy and discolored looking, old looking.
You can wash light things with a white towel, just something to make the load worth doing. This won't cause any damage to the clothes or the towel.
You can also wash each one completely separately, but that's a waste of water and laundry soap. You can potentially wash the shirt and jeans together, if the jeans are light enough. We're talking white, nearly white, or VERY light wash blue. Blue jeans will bleed into anything they come in contact with, especially in the wash.
Remember to always wash on the coldest water setting possible, too.