Supplies needed on-hand for current model water heater replacement?

I've got a new water heater being delivered tomorrow (Atwood 6 gallon XT model), and I plan to install it myself, replacing our current Atwood on-demand unit. Before I get into the removal and replacement, I'd like to purchase everything I'm likely to need. Other than tools and teflon tape, what should I pick up in order to be prepared?



Thanks!