There may be cases when a store needs to sell items that are not part of the WooCommerce inventory. Below are two options for selling 'miscellaneous products' in WooCommerce POS.
Create a POS Only Miscellaneous Product
Using the POS Only feature, you can create a 'miscellaneous product' for use in the POS. The title, sale price, regular price, tax rate and meta information can all be changed on-the-fly during checkout.
Edit the Miscellaneous Product in the cart
Edit the Fee line item
Using a Fee line item is similar to creating a POS Only Miscellaneous Product. Cashiers can quickly update the title, price and tax rate of Fee. The main drawback is that Fee's may appear separate to products in your reporting.