Yeah, give him a reasonable deadline for picking up the stuff you’ve found recently - make this the final opportunity for him to pick his stuff up. You could sell/pitch anything else you find later on, rather than contact him again. If there was anything he’d desperately wanted to keep with him, he’d likely have already dug it out and taken it. And if there was something he wanted but didn’t dig out? It’s just going to be collateral damage when you purge his belongings from your space. Consequences!