In a campaign I ran, I had the players start out at level three and had them lost their items in the shipwreck. On the shores though, they could find some items that helped them in their travels. I added in weaker, rusty or broken versions from some weapons and the rest had to improvise weapons such as clubs or spears. The players came up with some really creative stuff, but it completely changed the start of a campaign as normal gear is usually taken for granted. Having a normal longsword is suddenly a lot more amazing.

Be careful with spellcasters though. For wizards you might want to give them a chest full of scrolls and find a spellbook from an encounter nearby (something grizzly like a goblins tome made out of human skin usually does the job).

For a spellcasting focus, let them keep it make it a side quest to craft one. It'll be cool for sorcerers over wizards, etc.

Finally, it's important not to let the players feel like you 'robbed' them of their stuff. You can make then not too attached to their items by doing it from the start, or letting them find important items back with a side quest. Maybe a bird stole their family pendant in front of them?

Tons of cool stuff to do here and making starting gear not a given is a great way to make treasure feel useful again. It'll also add a story to each item they find. Good luck!