I was deployed on TF 3-08 and there wasn't a guy with us that used the issued kit. The only exception was our PPE. All PPE must be issued no exception. We were told that if we were to use non issued armor, IE dragon skin and were to get hurt we would not be covered financially. but it wasn't an option to use it anyway.
I had my own load bearing stuff, sling, gloves, boots, knives, tools, and we even purchased AGOG TA31A from some Americans.
This is within a Canadian infantry battalion. once we were back home all that kit was stashed and we went back to the issued stuff.