Is it a constitutional right to own a suicide vest? Do you need a sanity certificate to purchase one?

Suicide is illegal in many jurisdictions so a sanity certificate wouldn't be much help. The suicide vest becomes one if there are explosives and/or shrapnel attached. Explosives are usually illegal to just own by civilians as well, as are the detonators. If you just want to own a suicide vest, then consider that practically every jurisdiction will have laws regarding improper storage of explosives, especially if the detonator is right next it.

Also, the very fact you don't realise any of that probably means that the sanity certificate won't be as obtainable as you might hope.