Custom Checkbox fields can be added by clicking on the Plus button in the Field manager, on both Organization and Event levels, and selecting the option Checkbox in the dropdown offered.
Planners can edit the name of the field (e.i. Traveling alone), label for the field visible to contacts and participants (which may or may not be the same as the name of the field, e.i. Are you traveling alone?) and the category the field belongs to (e.i. Travel Information).
There is no further validation needed for this field type.