Occam's razor leads one to think that there is an obvious textual correllation from one hand-pimped thing tonthe next. In other words, a simple keyword based 'related to' algorithm, rather than a deep understanding of why you didn't want the flashlight and offered you the batteries instead.
One obvious thing I've noticed is that whoever is serving ads to me (on YouTube for example) has an idea about my sex. A few months ago I did some research on period tracker apps (i.e. products exlusively for women) and immediately noticed a burst of advertising that assumed I was female.
Adsense bidding is going to offer advertisers advertising options based user profiles which are somehow anonymized. So it's not a case of falling into a "cluster": even though I'm a typical male in other respects, the strong correlation of certain pages/searches with particular gender-specific interests swamped everything else and made me apparently attractive to a new set of advertisers.
Any ad for tampons shown to a guy is a waste of space. Its in their interest to classify you by demographic as much as possible. Google has (had?) a page where you can view all your data and they had a list of all your interests (according to your searches presumably).
