Membership certificates, seal for LLC

[Bienes Raices]

I've noticed that these corporate kits for a new LLC usually cost from $50 - $100. I would like to save some money and just buy a binder at an office supply store. I've read on some sites that the corporate seal is not necessary or used that much in real life. Is that so? If not, what documents do you stamp with the seal? Also, do the membership certificates need to be formalized and created by some other company, or is that something you can do at home for free on your PC?