Multiple options, any or all can be selected, one required

[split63]

How can I set up multiple options such that at least one is required, but one or more can be selected.
I used a radio button approach which forces a selection, but only one option can be selected
I then tried check box, but it does not force a selection on the product page, but rather displays a warning message on the shopping cart page.

[balihr]

Radio buttons are intended to be one-only, and check boxes are intended to be optional. If you want to force min one check box, you'll need to add some jQuery. Take a look here or here.