shabbos

Question

In my previous post regarding being in a car on shabbos you seem to have mentioned two issurim 1) amira L'Akum and 2) traveling out of the city boundaries. If a non-jew is going shopping and will be within city limits can I travel with him since hes doing it for his own reasons and then walk from where he drops me off to synagogue? Or can I go in a bus if payment arrangements are made before Shabbos?