Well, you can claim for all legimitate expenses.
If you're VAT registered then you can claim all VAT back on legitimate expenses, with VAT receipts, or normal receipts if no VAT receipts available (sometimes on small purchases in Tesco, or mobile phone prepay credit for example)...you must also charge VAT if registered.
Any legimitate expense can include a portion of household expenses if you work from home, like heat,light etc.. this may have a Capital Gains implicition when you sell your house, it may also have insurance issues, .. if you rent it may be against your lease to work from home.
VAT can't be claimed back on petrol, even if legimitate, except possibly when used in a generator, or garden tools for gardeners... not sure, but can't be claimed back for use in a car.
There are no mileage allowances or anything like that. Food, like lunches, is not allowable, as you eat to live, not for your job. The exception may be when working away from your usual base, like staying overnight in a B&B when doing a job in Waterford, and paying for meals while staying down...
Your phone bill would normally all be charged to your trade.. both the VAT reclaimed, and the ex-VAT entered as an expense, and taken off your profit,...
Your car, and all associated expenses could likely be completely used as legimitate expenses... you should probably allow a portion of private use, say 20% or 40%, but this probably isn't necessary, especially if you have a second car for private use, or you drive a van with commercial tax and insurance..
Some big expenses, like new cars, or big machines, are not expenses.. but you claim VAT back when paid, and the ex VAT part would normally be completely taken off your profit over five to eight years say, as depreciation each year... say 20% per year over five years.
Business cards and all that are allowable... and pens and tippex for the office.
You need to ask specific questions... about what you're thinking of doing.. your accountant may be vague as it' pretty simple, you can claim for practically every expense you incur while doing your job, except food and clothes, and you can't claim for anything else...
I'm not an accountant by the way,.. and I don't always strictly follow all the rules,.. like... I'd claim VAT back no problem on mobile phone credit even if the VAT wasn't displayed..