Yeah I tend to side with Junk, I don't waste money on "cheap" guns that I know I probably won't get kills with, I save up for the next round by buying a pistol.
I'll buy a shotgun if I've had a lot of caffeine and I'm feeling hyper though >.>
Also, I'm binding kill in console right now, mass suicide FTW.
I dont have any buy binds in Source but in 1.6 I used to have the keypad all bound up.
1 would buy an AK or a kit + M4 (b/c they're team specific you don't have to waste two keys, just write a script that tries to buy both) (plus it helped me remember my kit for scrims

)
2 would buy a kevlar/helment, kevlar, deagle
3 - 2xflashbangs, 4-hegrenade, 5-smokegrenade (like someone else said, thats how they are on the menu)
and I used to have 6,7 bound for primary and secondary ammo (I'm sure y'all are too young to remember the days when you had to *gasp shock horror* buy ammunition!!!!

)
Now that I think about it, I miss my binds.
I also had that CS helper, you hit H and a side menu came up, it had map specific calls, server RCON commands, the radio commands, that was some cool stuff. (oh and I customized it to have all my funny inside joke binds

)
Sadly, CS:S does not have any such menu plugin D: