There are a lot of useful characters in the extended Unicode character sets, covering both foreign languages and a large number of useful symbols. The following are some of the special characters used in other documents. All the Unicode characters can be looked up here: https://www.compart.com/en/unicode/

Name Character Codepoint
Cubed (^3) ³ U+00B3
Double-Chevron (Left) « U+00AB
Double-Chevron (Right) » U+00BB
Double-Square-bracket (Left) 〚 U+301A
Double-Square-bracket (Right) 〛 U+301B
Ellipsis / Ellipses … U+2026
Omega (Ohms) Ω U+03A9
One-eighth (1/8) ⅛ U+215B
One-half (1/2) ½ U+00BD
One-quarter (1/4) ¼ U+00BC
Squared (^2) ² U+00B2
Three-eighths (3/8) ⅜ U+215C
Three-quarters (3/4) ¾ U+00BE