I never thought buttons on either side of the mouse wheel would be so useful. Now I can't imagine using a mouse without it. (More about the key binds in the comments) :
Guide to Keybinding in MMOs for PVP and PVE | Taugrim's MMO Blog
Best Fortnite Keybinds (2024 Update) - Setup.gg
Best Keybinds for People with a Normal Mouse (x-post from r/FortniteBR) : r/FortniteCompetitive