I guess it depends on how long you've had your materials.
FIFO: First In First Out
Works best if you're turning stuff fast because you end up with the most expensive stuff for next year.
LIFO: Last In First Out
Works best if your supplies are mostly old and the new stuff cost a lot and you want to minimize your income (decrease tax liability) by having a big Cost of Goods Sold expense this year.
Thing to remember is you can't change from one year to the next - you'll have to pick what you want for this year and stick to it.
LIFO is a good first year gambit and lets you have the larger expense now, and that's true every year.
It means the supplies on your shelf are always the oldest ones you have, and therefore the cheapest.
(Keep in mind this is only a paper distinction - no one knows when you bought the actual stuff you're using. This is only a receipt thing.)
You should keep all your receipts! IRS doesn't audit many people in low income brackets (why bother?) but there is a random element that can make you very unhappy. Always be conservative in your tax returns. The ideal would be to have an IRS audit and have
them owe
you money... Pretty unlikely though.
If this doesn't make sense I apologise, real tired today...
Dave