What sort of insurance? Life? Health?
This very reason is why many workers don't retire until they reach 65.
Are you eligible for health insurance under COBRA? If so, that will get you the same insurance you're leaving for a max of 18 months. Otherwise, you'll need to contact an insurance broker for three years' coverage. I'd do that ASAP. If it's not too late, you may want to hold on for a bit until there is an open enrollment period.
It will set you back a bit, though.