As the name implies, a combo system picks and chooses elements of both the paper and electronic systems. Combo systems are highly idiosyncratic, but here are some possible combinations:
Idea #1
Use the paper system for p-card; use electronic for everything else.
Idea #2
Use the electronic (spreadsheet) version of the reconciliation report with paper documents.
Idea #3
Use printed reconciliation reports with electronic records; use paper p-card system.
The main idea here is that bits of one system can be combines with parts of the other to create something that works well for the department.