Yes vitamin k is good for bruises and spider veins.. But will not help much for scars or stretch marks.
100% cocoa butter (palmer's is ok) will do wonders for stretch marks, but you can't just put it on your skin like a skin lotion and expect it to work. You must rub it into your skin until there is virtually nothing left, and do this twice a day. It will reduce stretch marks a great deal, if not make them disappear all together.
Vitamin e is your other solution, for both stretch marks and scars. (i.E. Older stretch marks that have left scars, or acne scars, etc.) however, use 100% pure vitamin e oil and rub it into your skin. The most inexpensive pure vitamin e you will find are the capsules from any health store. Usually you would swallow them with water. But if you crack open the gel-caps in your hand, you will have 100% pure vitamin e oil, no additives. Rub this into your skin. (it's odourless) and watch your scars disappear... You will have noticable improvement in only a few days, and most light scars will disappear in weeks.
Finally, if you're still worried about stretch marks... Tanning / tanning salons will help even out your skin tone.
If you have any questions, feel free to ask.
Justin