Carla, we had the same April Yosemite experience a few years ago!
we have almost the same pics. it was 73 degrees and sunny the first couple of days and then a cold storm blew during the night, dropping 3" of snow in the Valley.
as to what you can leave out, the bears are used to anything looking like a cooler, as possible food. even a water jug.
and don't leave anything outside, like grills, stoves, containers, that could have had food on/in it.
agree about even April getting booked up quickly.
and Zoe the Wonder Dog(R.I.P.)
'07 Roo 23SS pushing an '07 Chevy Avalanche
Equalizer WDH and Prodigy BC