3 Answers

yes most definitely receipts, documents etc anything that may relate to missing/stolen items. Proof of who you say you are etc. Warrants give the police rights that is why they have to be applied for. 

Excellent question. This would have to be set forth in the warrant, at least in the U.S.. What would happen if an authorized/unauthorized gun was found in the drawer, and it was determined that the owner killed somebody with it? The owner could've committed 1st degree murder, but the evidence would have to be suppressed. I was in law enforcement.

I have heard of warrents being extended when items are found that are related to crimes not included in the original warrant. ie: looking for drugs, finding stolen property, stolen cars etc.