It is always sensible to keep a good reserve of emergency food, water, fuel, and other essentials. If possible also keep a reasonable stock of useful though not vital goods such as liquor, tobacco, confectionery and non perishable consumer goods in general.
We all have the essentials, but it's hard for me to figure out what to stock up in case of a global shipping slowdown. The only thing I can think of is electronics. But I'm just one person. How many iPhones do I need?