How do I add a column to a Contribution Summary report which will show the date and amount of the most recent payment/donation?
I recommend the summary fields extension:
https://civicrm.org/extensions/summary-fields
It'll keep a calculated copy of the last contribution amount (and many other useful fields) as custom fields of the contact, making reporting like this much easier.
Because contributions are stored in a separate table, generating fields like 'last contribution' tends to be complicated and mixing it with other values isn't going to be well supported in most reports, but pulling in custom contact field values is almost always supported.