problem with acc in the hat category and very LQ textures

They might be making preview with HQ textures or just have less uv islands that they can make bigger. Do not be tempted to put uvs in the space meant for extra clothing parts, there will be texture overlapping.
Another thing that plays a big role is how you unwrap the mesh. Things that need extra definition should be bigger ( the picture of flowers ), while things that do not need it ( the frame or the backside of the polaroid pic) can be smaller. If certain things have identical texture, you can map one over another.

It is best to unwrap each part( like, the lens ) of the camera as one uv island instead of each part of the lens to have its own uv island.

I don't see a point in re-doing the uvs now to stack them since the item is already high-poly. This should have been done in the process of modeling.