When I got back into the hobby I was impulsive sometimes because I could not believe how much product there was.... all the choices of road names... track systems, locos with sound, buildings and what not. I was in awe and went to the trains store sometimes twice a week, just to gawk! I made a few purchases that I probably did not have to have but I did think before purchasing most things, especially bigger ticket items. I put some engines on layaway because I thought I'd never see them in that particular road name again. I would purchase items that I never thought that I would see again ... I don't consider this impulsive but rather the clever thing to do.
I have stuck to my rule of always paying with cash and not credit card.... and on the few times that I have charged train items... I, upon arriving home. wrote out a check for the amount of the purchase and mailed it to the credit card company.
My purchasing of locos and cars has slowed down alot because I have pretty much all the train I want. At times if I see something that I'd like and its at a great price, Ill buy it.... but the price has to really darn good.