You can spot the rarities from outside of the crate by noticing the colors: You can also find items inside the enemy crate when you, your teammates or other enemy finish the knocked down. You might need to look around first because enemy can also see it.
This supply bin will provide you items and some time weapons as well. Supply Bin located around the map, near town, middle of nowhere, next to beacons, and more. Items can sometime be found inside houses, or other structure ground. Items on the ground consist of many rarities since it is depending on RNG. You can find Items on the ground after you landed.
Since items are all over the map their are some area that you can find high tier items. There are 4 different ways for you to find items in Apex Legends.