Keep them separately.
You can always combine your totals where necessary and it will save you the time consuming task of doing it at tax time.
Good advise Keycon! No matter what type of expense so long as it is business you should keep track of it on a monthly if minimal, if not at least each day. Waiting on January to come around and then allocating the type of expense might prove overwhelming, unless you have a good memory. Yes the IRS has updated its regs on business activity, but for the most part same principle applies, in the accounting world that is.