Do your neighbors above you have anything installed to prevent dropping things upon your head? Probably not, or you'd already have the answer to your woes. I'd either throw down some rubber matting or just try my best not to spill anything.
I'd have to guess if you were rather spill prone, you'd probably spill something a couple of times every few months, how many times of those would be outside (Probably a low percentage.)? Furthermore, how many times would those be outside with your neighbor also outside (based upon the percentage of time your neighbor and yourself spend outside vs inside simultaneously? Also probably pretty low.)? Statistically, the odds of this happening make it a negligible issue, I would believe.