Two options:

1. Use the Crysis suit menu hotkey ("V" by default) plus a combination of numbers.
2. Or better yet, if you’ve a mouse with programmable buttons, use macros. This will allow you to assign each of the Crysis power suit functions to just one hotkey.

Here's the video guide; it's pretty straightforward:


There’s a third option but it involves enabling the “Suit Shortcuts” menu and a combination of double taps, which I really don’t like. Double tapping movement keys to enable a suit mode isn’t really my thing. I find it's just ridiculous having to double tap crouch to activate stealth. It's silly.

It’s a matter of preference though and if you’re interested in it, there’s a guide on YouTube for that by Stanley Setiawan.