Can I use my Apple gift card in a store and combine it with cash to make the total payment?

You posted in the iTunes Store forum so I assumed you meant the iTunes and App Stores. Here's the information for the Apple Store.

https://www.apple.com/shop/help/payments

"You can use up to eight Apple Gift Cards at a time when you purchase online from Apple, or if you’re placing an order by calling 1‑800‑MY‑APPLE. You can use your gift card(s) with one credit card and your Apple Account Balance to pay for your purchase."

You can combine payment methods.

How App Store and iTunes Store purchases are billed. Click here --> https://support.apple.com/HT201359

"Which payment method is charged?

When you buy items or pay for subscriptions, Apple automatically attempts to charge your payment methods in this order:

1. Apple attempts to use your Apple ID balance to cover the full amount.

2. If you don't have Apple ID balance, you don't have enough to cover the full amount, or an item cannot be paid for with Apple ID balance, Apple attempts to charge your primary payment method (typically a credit or debit card, but varies according to country). The primary payment method is at the top of the list in Settings on your iPhone. You can control which payment method is at the top of the list.

3. If there's a problem with the primary payment method, or if the primary payment method can't be charged for the full remaining amount, Apple attempts to charge your other payment methods in order from top to bottom. If none of them can be charged, Apple may try again.

Yes you should be able to do that, because they accept cash or two different cards if need be.