Custom Add-ons

Hello, we often customize a trip for clients where we add on certain amenities or activities that aren't generally available or is a one-off from our normal trips.  We've created a simple custom-add-on booking item that has unlimited inventory and pricing in increments of $5 which gets us what we need.  Ideally, we'd like to have staff enter in what the custom item(s) are when they do that via a text field.  Right now, we're having them add to a 'Notes for your trip' on the booking form, which works, but is not ideal.