Can you go to post office right before Shabbos and overnight a package where there is guaranteed delivery on Saturday by noon.
Please explain and give sources.
Secondly,If you are staying in hotel and boss jonnie tells his non-Jewish worker they forgot to plug in the warmer . Go plug in now so they will have hot food. Can you eat the food?
Giving a package to the post office on erev shabbos in order to deliver it overnight, means that you are essentially telling them to do melacha for you on shabbos. Even though the gentile is being paid for the work, nevertheless if he is doing it specifically for the Jew on shabbos, and even though the gentile is being paid for the job and not by the hour. See Shulchan Aruch O:CH 247-1, 252-2.
See Commerce and Shabbos pg. 140-145 for some possible options when there is a pressing need.