My last two purchases have both been non essential but I could not be happier.
First I got myself an iOptron iPolar with the adaptor for the HEQ5 Pro. No more crawling on the ground getting cramp in my neck trying to polar align. I now sit comfortably next to the mount with my laptop on my lap and its done in a matter of seconds.
Yesterday I got a Pegasus Pocket Powerbox as I was getting fed up with the number of wires. I also needed a dew heater and there is a controller with two connections built in. It is also Indi compliant which fits nicely with my setup. I still use a DSLR so the 8V connection is ideal and I am using 2 UBEC's from the radio control world to provide 5V for the StellarMate and the USB hub. I now have everything mounted on the scope and only one wire coming off the mount which is either the mains 12V power supply or a battery if I have no access to mains. The argument I often see against a powerbox if that it is easy enough to make at home but if I were to make a powerbox it would be much larger and heavier so for me it was well worth the investment.
Neither are essential but they should help me spend more time and energy collecting photons than setting up equipment.