... pre-war things... are often more valuable....
.... for books, if it says "First Edition", these are valuable... but also depends on other factors.
I am a collector... I have first edition books of some authors. You can research this online...
Figurines, old books, farm machinery as well... can be valuable or highly collectible, or sought after.
Some things from Japan, may say "occupied Japan" or just have Japanese kanji "signature" markings or stamped impressions on the bottom. This itself, says a lot about the piece and/or the value of it, as a collectible.
If you have feudal era Japanese "pottery"... only an expert can valuate these... properly.
And "Meissen" pottery, can be very valuable! It is German pottery porcelain.
The thing is, your Grandfather collected these... while serving in the war. And, many things from this era... is valuable... or at least highly collectible.
Personally, I would NOT trash any of it. Nor, put it out for garage sale prices. Unless, you know, that it is junk.
If your Grandfather was specifically collecting things of a certain caliber... then even more so, it may be valuable. But if things are mass produced... these are not as valuable.
So many factors, determines if it is 'valuable' or just a collectible that is sentimental... or something that is historically significant and thus, valuable.
If anything, research the pieces online...
I wish I could look at it... I collect things.
What you might do is... take it to an antique store... and 'sell' it to them... or at least get their opinion on it. I have done that before. BUT... NEVER EVER, leave your piece there... or you may never get it back.
Next, take photos of everything you can... thus creating a photo file of it.... and thus, 'documentation' of it. And note down anything, in a notebook about it etc.
Or, you hire an auction house... to 'sell' your estate items for you.... they, often have appraisers on staff.... and because it is an auction house... they will keep a level of professionalism and quality standard, about your items... and YOU designate how low/high you will sell your pieces etc.
Since you seem to have SO MANY things to 'sell'... I would not do it yourself out of your garage.
all the best,
Susan