What numbers from last years return will tell me what additional charitable contributions I can or should take for this year?

[tygrtchr]

Charitable deductions are on a year-by-year basis.  If, however, you carried over contributions from a previous year that you were not able to deduct  because they exceed your adjusted-gross-income limits, you can deduct the excess in each of the next 5 years until it is all used, but not beyond that time.  From your question, I gather that you didn't have carry-over contributions.