Likewise, Crypto is a mystery to me.
As for 'solid, physical' assets (like a car and gold), they may be subject to Import Duties and VAT upon importation into Thailand. As for the watch, perhaps wearing it when entering the Kingdom may work as personal effects.
I understand such items are regarded as moveable property, and are not subject to Income Tax upon sale in Thailand if they are privately sold (ie. not in a business activities).
As for stocks/equities, if sold overseas the question is the tax treatment of the proceeds if remitted to the Kingdom. I'm not aware of any ability to have stocks held via an overseas account transferred to a Thai Broker.