Limits to Strategic Stockpiles

Are there any upper limits to the strategic stockpiles I can build for my country?

Can I just buy 100 years worth of some cheap food and let that be that?

Can I store staggering amounts of weapons/corp supplies for later use?

Anyways, any limits?

Also, things that are of a time-based "favor" nature like services/air transports/construction, can they be stored in huge amounts as well?

There is no limit to everything you mentioned. However, if you stockpile active weapons in your country (i.e. not deactivated) you will pay maintenance costs, training ammo costs and salaries, as they will need LLWs (Soldiers) and MLMs (Officers). These people will be missed by your infrastructure and your factories. This goes for all weapons, even if they are not used in formed units, but just "lie around". But it doesn't apply to enterprises (no cost there), only countries. Other than that, all other stockpiles are free of charge.