Over two major careers, I have shipped a lot of items, both large and small, and even worked as a Rural Mail Carrier, learning the package business from all sides. These are a few tips for using the USPS(US Postal Service) to mail small and medium size packages within the US, particularly coin related items. Now the Packing hints apply to any shipping, rates here are current for the US only.
General Mailing TipsFirst off, Please LABEL your package correctly and legibly. A regular seasoned Route Carrier usually recognizes a transposed address digits, but any mistakes in Zip codes and Street names, including designations (Ct, St. Ave) and other IDing info are usually a must. I would be able to put a name to an address, sometimes, but don't rely on the carrier to do YOUR job! You would be surprised at the amount of mail that get UAA (Undeliverable As Addressed) daily. Also, loose packed materials, will get jostled around, secure your goods VERY well.
Shipping Tips:Now,I go the cheapest possible to ship and protect the products. I use the mylar flips over the 2x2s. The biggest factors are thickness, slightly lesser weight, and NO STAPLES. If you look at the pix enclosed, I have coins in a whole two pocket mylar, or in a cut half using tape to seal the opening(med paper tape you can write on) I usually try to put items in a plastic bag, to keep from moving around. I have at times used Tubes or paper wrappers for rolls of coins, but thickness is a factor there, quarters and above will need a bit different way than what is presented here.
Lets start with cheapest, the standard 1st Class Mail envelope. One 50c stamp mails 1 oz, each additional ounce is 21c stamp. This usually works for up to 10 cents, 8 nickels and maybe two halves at the most. I take a plain piece of paper, tape the flips to the paper, write a note etc. It helps if you write on the envelope "Hand Stamp Only!". This then doesn't go through a sorter, which can be hard on the letter, tear it up. I usually put a 21c stamp on it for good measure if I'm not sure.

Now, let's take those halves pictured. There are ten sets of them (20). I will be placing them in a bag then in that small padded mailer. I use two pieces of thin cardboard as further padding. (use one of the Priority Mail envelopes, cut up). This will go First Class mail w/Tracking for $2.75-5.50 depending upon weight This is usually the best way to go for above 4 oz of coins. Now, if the weight of this package is a lot, the price may jump to $7.00 or more, DO THIS then if it does. Put your parcel in a Priority Mail envelope and use that service. Priority Mail is a fixed rate shipping, the "if it fits it ships" kind. The envelope is $6.65 tracking and insurance included(US only) and is a guaranteed delivery time of 2-3 days (1st class is 2-8 days). I have used the envelopes to send folders, albums, and rolls even. just make sure contents are padded as recommended above, even more bubble wrap.
The next levels of Priority Mail are the three sizes of boxes, small($7.30), medium($13.70), and large ($16+ Not shown). I've never had to use the large, the Medium fit those 5000
LWC"s and will go up to 70 lbs! The small box holds a baggie size of 1200
LWC's at 7.5lbs. When using any of the mailing products, use tape to seal the edges well, and if heavy, strapping tape in a three dimensional direction! Inside, always make sure the item(s) don't move around, that the weight is fairly distributed if possible. Pack around the outside edges with bubble wrap or other packing materials. I save all my received packaging and reuse it. Make sure if using labels for addresses these are secure, use tape if in doubt.
Hope these help those who have never done much shipping and handling of parcels.