What is normally not acceptable to budget in a grant

I seem to have much more freedom in industry sponsored grants, so this is specific to government grants. I have never been allowed to budget in a 'Computer', but I can budget in 'a CPU'. I mostly work with computation, but I assume the computer issue effects many fields. I also cannot budget in tables and chairs, but through overhead from the institute I can buy those.

Are there other issues for budgeting funding for items that are not allowed that may be more specific to fields?

For example, are there usually restrictions on a microscope, for people in that field.