These are a few items that I would say are a good idea to have however they aren't necessary.

1. Spare cage
If you ever have a sick rat or get some kittens to introduce to your exsiting group then a spare cage is good idea. I would recommend something like a Critter 1 as these flat pack into the base so make storage easier.

Critter 1

2. Common Diseases of the Fancy Rat handbook
This book was written by Ann Storey who is the Life President of the National Fancy Rat Society.
An excellent and useful addition to your bookshelf, giving a description of all the common rat diseases, also covering nursing care, accidents and drug treatments

3. The Scuttling Gourment
Written by Alison Campbell and the book provides a comprehensive guide to wholesome nutrition for rats, and includes such topics as calorie restriction, scatter feeding, specialised diets to help in the treatment of illness, the soya debate and dietary deficiencies. It contains quotations, anecdotes and information from many sources, as well as representing many hundreds of hours of her own research and reading into the subject and it is well referenced throughout.

4. Dr. Squiggles - Daily Essentials 1
Daily Essentials 1 is a water soluble, small animals vitamins and minerals. My rats love this and I offer it twice a week. There are others suppliments available from the same company for all sorts of reasons.

L-R: Daily Essentials, Calcivet, Guardian Angel & Poly Aid

5. First Aid Kit
A basic kit is a good idea to have in just in case something does happen you have things available to hand. Items I would recommend are:
Anitbac Powder - sprinkle on a wound to help stop infections
hibiscrub - helps to clean out wounds especailly good for abcess
Purple Spray - helps prevent infections in wounds
Nutrical - a paste which is good for poorly rats to encourage them to eat.

6. Treats - dog chocolate drops, dog biscuits, seeds, fruit etc
It's nice to have a few treats every now and again but don't go too mad and overfeed them. Dog chocolate drops make nice rewards and there are so many items available now. I make treats for my rats and you can find more details on my feeding pages.

7. Litter tray (if you wish to continue using or wish to start)
I do my best to litter train my rats to help make cleaning quicker and easy for me. Rats tend to pick this up quite easily and more or less stick to it. I find it works best if you use a different substrate in the litter trays to the main cage.