Crackers are used in the meatloaf to lighten the texture and to add moisture, in addition to binding the meat loaf together.
So you either need to use crackers or you can use bread crumbs instead to make the meatloaf with.
If you don't use either bread crumbs or crackers the meatloaf may not hold together and come out badly but you can still eat the meatloaf without the crackers or bread crumbs.
I've tried making meatloaf without crackers or breadcrumbs and the meatloaf didn't turn out as good but it was still edible.
The meatloaf just fell apart but the meatloaf will fall apart anyway once you eat it.
So if you want to make some meatloaf and have no crackers or breadcrumbs then you can make the meatloaf but be prepared for it to fall apart.