What you should be doing really other than just common sense guesswork is using Google's own tool to show you what is trending in search and looking at weekend spikes.
Example: Right now in the "Top Charts" / Travel & Leisure, "Martini" is #1 for cocktails. It has spent 113 weeks in the top 10. Drill down ('explore') and expand the date range to exactly 90 days, and you see that it's clearly peaking on weekends. (mouse over the peaks) (90 days is the best setting for seeing weekend trends)
Go check the search volume and you've got a figure to put to your fantastic guesswork. (glad to see my guess was right and everyone in the US isn't searching Martini cocktails on a Tuesday morning). Not sure why I picked cocktails - gayness starting to seep in again I guess.
If you want to push products look at the "shopping" trends. Top Retail companies being searched in Google are Amazon, Wallmart, The home depot, Lowes (home improvement stores).
Again - peaking weekends (Sundays). Go sell power-tools in your Amazon store or whatever.
The sensible thing to do is spend a little time harvesting the data however you do, putting it together in excel with the search volume data & your traffic data and run some basic reports / graphs to work out the best ROI with your various offers. Do this for a longer period and you will have more predictability in your sales. You could put a plan in place for an entire year if you wanted - can make better decisions armed with more information. Say you plan out a year or a few months - write a task list for each day. Fill your calendar up then you don't have to think about daily tasks again, instead spend more time thinking about how to improve profit, which is what your actual real job is remember.
People seem to forget about Trends, but it's basically a great tool that tells you what shit people want to buy and when! Sending out emails? Schedule your awebar / mailer tool accordingly. Tweeting people's lives into oblivion? You know when to hit them & with what.
Who was it that said "Sell shit people want to buy not shit you want to sell"? I agree, but I'd like to add "Sell shit people want to buy when they want to buy it the most"
Obviously you'll have to use the KW-specific trends search for things like dating or porn shit, but you get the idea.