Most well off investors take cards off the table to secure their best properties.

For example maybe have one phone number for post cards and a separate phone number for yellow letters.

I'm attending my first REI networking meeting tonight and realized I don't have any business cards.

Get a secured credit card.

Maybe attend some local REIA groups, pass out business cards, etc.?

Building a budget always reminds me how hard the student loans hit me and how terrible I was with credit cards.

You have to get a Lowe's and Home Depot Credit Card. 

Also get a credit card that has travel points and charge everything to it so that you can use them towards visiting property if you have to.  

Should I attract leads with yellow cards and wait for a call, or go and look for abandoned properties and try to find the owner of the property.

OK  If you dont have 700+ credit and can not get some unsecured loans/cards to flip at a much smaller unsecured rate/payment then use hard money, if the alternative is to sit at your day job wishing you were not there.