A few tips from my experience.
Carry rubbish bags and a small brush and shovel ( rubbish bags great for wet towels and i sweep up the hair and take it away with me)
A hose attachment for rinsing over sink
some consultation magazines/colour chart
band aids, nothing worse than cutting yourself and having to ask clients to raid their first aid kit!!!!!
toners such as schwarzkopf ice flower mousse are my saving grace, theyre fast and conditioning , sometimes trying to tone and apply at a kitchen sink is a nightmare, the mousse is quick and comb it thru while your waiting
details of your bank account number my clients often deposit the money via internet banking while im at their house.
hope some of these ideas are of assistance