Adding optional items to a quote showing price but not adding to the total price.

We repair electronic instruments and a lot of our clients ask for an optional extras e.g calibrations, new housings, cables etc. I would like to be able to have a quote showing prices but not adding to the initial total. and mark these as optional.

I have tried putting in a 0 quantity and other work arounds manually changing the word document and total the quote and manually working it out.

Thank you