90:2 Based on the phrase “you will honor (Shabbos) by not…pursuing your affairs” (Isaiah 58:13), the Sages explained that involvement in one’s usual affairs is prohibited on Shabbos even if it does not necessitate performing a forbidden labor. An example of this would be checking one’s property to see what it will require on the next day. Similarly, one may not walk through the city in order to identify a horse, boat or wagon that he wishes to rent after Shabbos if it’s obvious that he is going for this purpose. (If it’s not obvious, Mishnah Brurah 306:1 permits it.) One is, however, permitted to go out in order to guard his own property or that of another person.
90:3 One is not permitted to walk on Shabbos to the limit of the Shabbos boundary (techum) and to wait there until nightfall so that he may speed up his journey by continuing beyond the boundary when Shabbos ends. Since he continues on his journey from there after Shabbos, it’s obvious that this was his main intention in going there. This is only the case when one went there in order to travel to do something that he could never have done on Shabbos in any circumstance, like hiring workers, picking fruit, or bringing produce that is muktzeh. However, one may travel to the Shabbos boundary before nightfall in order to bring in his animal since this activity is not inherently prohibited; he could have done so on Shabbos were he not impeded by the limits of the techum. (This would only be permitted on Shabbos if he if retrieving it for a permitted purpose, such as to save it from loss. If his intention is to perform some labor with it, he may not do so in any event – Bi’ur Halacha 306:1 s.v. l’havi behemto.) Similarly, he could go to bring back already-picked fruit that isn’t muktzeh because he could have done so inside an eiruv. One may walk on Shabbos to a garden that is within the boundary in order to pick fruit after Shabbos because it is not obvious to others that such is his intention. Observers will assume that he went for a walk or to look for a lost animal and, once he was there, he decided to stay until Shabbos was over in order to pick his fruit. (He may not hang around outside the garden until Shabbos is over because then his intention is obvious – MB 307:39.)