This includes any small items purchased for the office that are specifically used in the performance of your duties as a company.
Computer or electronic consumables.
What's not included
No high value ticket items such as expensive MacBooks, PC's or Mobile phones - These should be capitalised and treated as assets.
How is it taxed?
All of the items within this category must be used wholly when carrying out your duties at work. Be careful not to expense anything that isn't necessary to you performing your duties. Also make sure things that are high in value are turned in to assets just so you're recognising the expense over its useful life. Hold on to those receipts by attaching them to the transactions in case the HMRC ask any questions!
As long as the employee needs what you are buying them to perform their job you don't have to report or pay tax and NI on the items.
However if you provide office supplies as part of a salary sacrifice arrangement it won't be exempt and will need to be reported on a form P11D.