Need to use receipts for "mdse for resale" bought in 2023. Those items did not sell until 2024. Need to deduct expenses. Should I use cash or accrual method or both?

You should use the cash method if your gross receipts are less than $26 million (see below).  The items you purchased for resale no longer need to be separated by the amount of inventory on hand at the end of the year (December 31st).  All receipts for merchandise for resale can be deducted from your current year income.  If you had a year end inventory in 2023, then you can use zero as your ending merchandise for 2024.  This will capture the remaining merchandise cost if it was not deducted in 2023.

The inventory or merchandise for resale at the end of each tax year no longer needs to use the accrual method if you meet the rules under the Tax Cuts and Jobs Act (TCJA) of 2017.

According to TCJA, businesses with gross receipts below $26 million (for 2021) are considered eligible to use the cash method of accounting for their inventory.  

• TCJA Comparison for Businesses: The law expands the number of small business taxpayers eligible to use the cash method of accounting and exempts these small businesses from certain accounting rules for inventories, cost capitalization and long-term contracts. As a result, more small business taxpayers can change to cash method accounting starting after Dec. 31, 2017. 
• Revenue Procedure 2018-40 provides further details.