It is well known that members of the cucumber/ squash family can’t be grown side by side because they will cross pollinate.  However if you look at the Latin name of the variety you want to grow, as long as the name is different it is possible to grow them side by side and safely save the seeds (and have them grow ‘true’ to the variety you started with).  All the following have different Latin names and can be grown together.

Marketmore 76 Cucumber:  Cucumis sativus

Nutmeg Melon:  Cucumis melo

Sugar baby watermelon: Citrullus lanatus

Spaghetti Squash:  Curbita  pepo  

Burgess Buttercup:  Cucurbita maxima