I would argue that the main thing that most religions have in common is a set of ethical beliefs. I am not saying that all religions share the same set of ethics, but I am saying that most religions have some set of ethics and that they believe those ethics are mandated by some supernatural forces.
In the Judaeo-Christian tradition, for example, there are the 10 Commandments. These were handed down by God to govern the ways in which people behave. But other religions that are not that similar to Christianity have ethical codes as well. For example, many religions have elaborate sets of taboos that govern their adherents behaviors.
Another major common feature of most religions is ritual. Practically all religions have rituals that must be performed on more or less of a regular basis. These rituals are often the most public manifestations of the religion.
There are other commonalities, but I would argue that these are the most important features that are common to all or most religions.