I use the Air Optix. They suggest you change them every week or so, but I have worn them many times for two weeks. I carry spares with drops and a mirror as well, just in case. I worried some about backpack hunting for one or two weeks at a time but have had zero issues. I had more trouble learning to put them in with my big fingers, good to go now.
Like the others mention, stay hydrated and use your drops.
