Best value:
KENBU AirTag Silicone Case
This inexpensive case on a carbiner clip lets you attach your AirTag to just about anything. Just slip the AirTag inside; the Apple logo will still be visible. Choose from nine different colors.$7 at Amazon
Bargain four-pack:
SZJCLTD (4 Pack) Soft Silicone Case Compatible with Apple AirTags
You picked up a four-pack of AirTags from Apple. Why not pick up four keychains for one low price? You get one of each color, as shown, perfect for color-coding for different family members or for different items you re tracking.$11 at Amazon
Colorful silicone:
Sallydream Silicone Case for Apple AirTags