What did the Roman Senate usually discuss on a daily basis?

Any matter proposed by a magistrate, could be something simple like office elections, taxes, war, etc. The matter had to be proposed by a magistrate, then voted on by the senate. A Tribune could veto the vote, though, stopping it from proceeding any further.

Just a little addendum here. The question seems to assume that the Roman senate met daily. Not so. There were certain days when they were forbidden to meet and there were other days when there simply was nothing of great importance to debate and most of the senators did not bother going to the place where they were meeting. During certain festivals such as say, Saturnalia, the senate did not meet.