For me it's the Meggie Moo collars and the co-ordinating velvet leads. The leads are actually surprisingly practical - very strong, beautifully soft in the hand, wash like a dream and your dog will look as gorgeously aristocratic as they deserve. Go for the 6ft length. Ours have a collar collection - and you will find they have special ones for Christmas, days out etc... 
My other recommendation is to think about where they'll be travelling in the car, and if it's the boot, to make sure it's lovely and comfortable for them. The Princess and the Pea was actually written about a greyhound. Our estate car has the back seats down, a layer of two duvets in covers, then a topping of extra thick vet bed (highly practical as it washes easily is warm and soft and wicks away moisture). There is also a Milgi dog bed which I take to training classes and when we open the boot it's like musical chairs to see who gets to lie on that first. 
We don't bother with a crate though I know some people like them. The size you'd need for a grey means this would take over your house. Most of them are happy as long as they've got a comfy sofa.
Get a nice Yankee Candle for the farts (on a bad night you will swear you are dying of methane poisoning). Other useful bits - a clicker, a grooming brush (the Zoom Groom ones are nice) and what can be fun - a lunge whip that you can tie a little fluffy on to - hours of fun playing games with them. Some like squeaky toys but a lot don't especially at first - I'd wait and see.
There is a very useful FB page of Secure Dog Fields which is helpful if you are looking for somewhere safe to regularly play off lead until you get recall in place. A lot of greyhound rescues also offer sighthound playgroups and regular walks etc - the social side of greyhounds is awesome. We have made fantastic friends all over the country through our hounds.
Put your vet number into your phone - they will become very familiar. Not because greys are unhealthy (far from it) but they often have an amazing ability to get into scrapes and have very thin skin so always seem to be needing to be patched up.
Good luck - and welcome to the cult...