HMRC's website should answer most of your questions.
This is a Fixed rate expense allowance available to uniformed airline crew. It substitutes for the submission of a variety of variable expense claims.
There are a number of capital expense allowances where tapered relief may be given, however it is unlikely you could claim for a notebook or for a headset, unless it is a noise cancelling headset where no alternative provision is made by your employer.
There is no provision for "food & drink" under the FREA. I think you may be confusing the recent submission audit conducted by HMRC in respect of the taxation of aircrew allowances, where these elements were in part included in those submissions.
Food and drink, do not normally pass the "wholly, exclusively and necessary" tests for submission as allowable expenses for aircrew.
The website should help.