Can I add a space for people to write notes: like dietary needs and or comments?
I have done this with custom field set for individuals with two fields, one a multiple choice (All, Vegetarian, Vegan, Special) and the second a text field to show anything else. I also included disability (yes/no field and a text field for detailed requirements in the same field set as both sets of info are needed in relation to courses booked. There are lots of ways to do it and the user documentation tells you all about custom fields.

Having the structured and unstructured fields allows you to search, but also include additional information.