Re: Odd product combination - so which category ??
The best way to expand is to compare the submitters' guidelines (which says submit to one category, without exceptions) and the editors' guidelines (which allow additional listings at the editor's discretion.)
There are specific kinds of "deeplinks" or "multiple listings" which are SPECIFICALLY DEPRECATED. One of them is
"Single-product-line listings of retail shops."
That is, it is the editor's responsibility in a case like this, if at all possible, to limit the site to one Shopping listing by choosing a suitable category and description. They would consider possibilities like:
1) Business owner of site sells 8 different mattresses and one tricycle: List under "Bedding" but mention in description "also sells tricycle"
2) Business owner of site sells 5 different mattresses, two tricycles, and an assault rifle. Listed under "miscellaneous klitch" with all three lines mentioned in description.
This is not an absolute prohibition, but coming in the door trying to get multiple listings puts you in an adversarial position with the people you are hoping to convince to help you -- imprudency squared.