Before I got my grain mill, I was buying pre-crushed grain and there were a few times where I took advantage of those NB "buy 2, get one free" kits and by the time I got around to brewing the last one, the efficiency was lower than expected and the beer just did not seem as "bright" as it would if I brewed it within 2 weeks of recieving the premilled grain kit.
I chalked it up to the grain getting stale as sometimes it would be more than a month before I could get through 3-6 kits grain-wise depending on how many kits I picked up.
With having the grain crusher, I keep my bulk 2-row/pilsner in food grade 5 gallon buckets with gamma lids in my brew shed at 75 deg and crush the day before brew day. No more stale grain issues.
Not sure what the lifespan of uncrushed grain is, but I think (and from experience) that if you keep it in airtight containers(keeps bugs out) and at a decent temp, it stays good for quite a while.
Plus having the grain mill allows me to know how well my grain is crushed everytime.
As far as yeast and hops, keep those puppies in your fridge until its brew time or starter making time for your yeast. You do NOT want to have those in a non-refridgerated environment if at all possible to keep both the yeast healthy, alive and hops maintaining their freshness. There is a reason every LHBS I know keeps their hops(outside of the extract kits) and yeast in a fridge.