It depends but you will be able to deduct supplies as a business expense even if you do not have any business income. (This applies to all eligible business expenses. Please
refer to this IRS link for more information about Business
Expenses )
As for inventory, you include inventory at your cost amount (what you paid for it, not what you will sell it for). Inventory will remain on your books until you sell the inventory. Then you will usually include the original cost of the inventory as part of your cost of goods sold (and any remaining unsold product would be
remain in inventory). However, as part of the small business exemption, these
items that would have been included in the business inventory may be deducted in
the year that either the item is sold or when it is purchased, whichever is
later.
This
exemption from recognizing inventory applies to sole proprietorships
or very small businesses. To be exempt from reporting inventory, an individual
taxpayer must not annually earn more than $1 million, as determined by annual
gross receipt amounts for the past three years.
Please click this
link for more information on IRS - Cost of Goods Sold and good luck with your business venture.