Finally got off my behind and culled through all the reference pics I gathered for my Liberty ship build. This is a sampling. Size and quality varies vastly.
As promised, the first one is the tug as deck cargo! :
Next we have the usual large wooden crates on some of the hatches, but not all. This one also has the longer booms for the torpedo nets that could be deployed along both sides:
Here we have some LCVPs as deck cargo, notice they are perpendicular to the hatches. This is also one of the few photos I found of a Liberty painted in any kind of camouflage, let alone a dazzle scheme:
Here is the Daniel Carroll with a full load of I don't know what on Hatches 2-5:
As you can see, nothing was wasted spacewise as far as stowing deck cargo:
The John Calhoun with what looks like ... structural steel and construction supplies:?
Excellent shot of a Liberty with a full deck load of P-47s, even on the No. 1 hatch:
Not a Liberty, looks like a tanker, but here is a deck load of P-51s and P-47s, showing them protectively wrapped, with additional canvas or something like it around the engines:
And finally we have the Peter Silvester with a full, and I mean full, load of 6x6 trucks: