Unfortunately there is not much you can buy out of actual made in Palestine product because of the blockade. For example this is from their Kufiya factory in West Bank

https://www.kufiya.org/

Due to high demand and short supply, we would like to inform you that many of our Kufiyas are now available for pre-order, and you can now reserve your kufiya of choice from our next shipment. Kufiyas that are available for pre-order are in fact ready and packaged in Palestine, awaiting shipment to Europe. Please note, however, that the delivery of your kufiya will only be carried out as soon as our next shipment reaches Europe. We appreciate your understanding and solidarity in this matter.

I don’t know if there are any Palestinian gross domestic products, but there certainly isn’t with the current state of their borders. Even if there were, you’re not exactly funding a regular defence force, you know?

Buy a genuine Palestinian kufiya and wear it to show solidarity with Palestinians while enraging any nearby Zionists.