Check out looked up value field options in FileMaker help.
You can load a table with typical transactions and then this option can copy the data into a new record in your main table when you make a selection from a drop down list or pop up menu. If you need to enter a non regular transaction, you can just type data into the fields.
Oh yes, if any of your regular transactions happen on a predictable schedule (every month for example) you can write a script to generate a new transaction on that specified schedule.
Thanks for the tip Phill
I'll try that