Make a .cfg named Buyscript and put it into the cstrike folder.
In this .cfg you type:

bind "F10" "secammo;primammo;defuser;vesthelm;say_team "
bind "F11" "awp;deagle;defuser;hegren;vesthelm;secammo;primammo;say_team "
bind "F12" "ak47; m4a1; primammo; deagle; secammo; flash; flash; vesthelm; defuser;say_team "

If this is done, open your userconfig and type this and save it:

exec Buyscript.cfg

Finish!

To use this script type in game:

F10 = This will buy you ammo, defuser and vesthelm
F11 = This will buy you awp, deagle, defuser, grenade, ammo and vesthelm
F12 = This will buy you AK47 or M4A1, ammo, deagle, 2x flash, vesthelm and defuser