Every so often I come across event listings inviting people to come and shred their documents for free or a minimal cost. In fact even places like Office Depot & UPS offers shredding services. On a side note, I just realized that they both use Iron Mountain for their shredding services.
Are all documents created equal? No! There are some that are advised to be shredded while others that are advised to be kept. For example, tax returns (from at least the past 3 years), investment records should be kept according to U.S. News. While items such as utility bills, ATM receipts, voided checks are all firmly encouraged to be shredded not just thrown in the trash. In short anything has personal information like your signature, SSN, address, phone number should be disposed of properly. FightIdentityTheft has a more exhaustive list on what should be shredded.
As far as boarding passes for planes go, I will let you be the judge of that. Yes, they do give out unauthorized information to people. However, just that information by itself may not have the potential to be an extreme security vulnerability. However, that information + the information from your various social media outlets could lead to something impactful. In general, especially with security I go with the mottos it’s better to be safe than sorry & prevention is the best cure. Brian Krebs wrote an investigative piece on what information can found from a boarding pass. The result is in the image below, and the link can be found HERE.