Level 4 Magus (Blackblade) with 6k gold to spend.
Typical Dervish build.
Str 10
Dex 18
Con 14
Int 20
Wis 10
Cha 9
Aasimar
Dervish Dance
Weapon Finesse
What should I buy?
Well some light armor of course. Then a wand of shield is something I found very useful for a low lvl magus of any sort.
pearl of power I is also a very good investment.
So far, I'm thinking
+1 Mithral Chain Shirt: 2100
Lvl 1 Pearl of Power: 1000
That leaves me with 2900.
No point in a weapon since I have my Blackblade.
I'm not sure if I want to waste gold on a wand that is disposable since I can memorize the spell Shield.
also a wand of infernal healing is not a bad choice since it is much better for wand healing then CLW.
Haversack is always a good suggestion but waiting a few more lvls isn't bad ether. You could save the coin so you can get a dex belt soon.