The opposite of picnic is... prison? And resurrection is... traffic jam?
Being illogical is probably the best thing you can do in a brainstorm. Or, to be more specific in my fostering of weirdosity: after you've exhausted the trough of ideas that make sense, there needs to be a point of departure where you seek out opposites.
Human beings have a tendency to find relationships between things whose meanings seem to be in direct conflict. The tension between those sparring words or images, and the ensuing friction in your mind, forms the sparks that ignite more novel concepts.
You aren't really playing with antonyms. You can see from even the barest examples that the idea of opposite is only a trick that we use to churn up concepts that initially seem far outside "the box".
Turn off your literal filter, start riffing off what's on the whiteboard or in your sketchbook, and see what new thinking takes form.