What are the "rules" about this? I often see people arguing against scab labor with real fervor, but how is this defined? And who decides where to draw the line?
e.g. continuing with the cafeteria example, if people decide to go off campus and purchase food at a different establishment, are those food workers then considered scabs? Or is it only scab labor if it's hired as a temp replacement by the company against whom the workers are on strike.
And back to the original example, what happens a person needs to get to the airport, or to work? The challenge with substitute goods and services (e.g. Uber or gypsy cabs or other app-based car services, in place of licensed cabs) is that a monopoly gets marginalized and a strike is less effective. But what's a person supposed to do who needs to be transported from A to B? Not call Uber?
It is a simple definition, a scab is a person who accepts work that undermines the union. This can be refusing to join the union, accepting less pay or crossing the picket line and working.
So a restaurant worker not refusing to feed a student off campus would not undermine the shutdown of the on campus cafeteria. But any attempt to recreate the cafeteria by the school, on or off campus, would.
You should do the best you can to do nothing that could undermine the strike. A key is who do you complain about and complain to. If public transit workers are on strike, which makes your commute worse, do you blame the workers or complain to the management.
e.g. cafeteria workers are on strike, so the org orders pizza instead - are the pizza makers and delivery people scabs? Or is that just a work-around?