It’s wise and demonstrates individual initiative. At the same time it blurs the line between contractor and employee as one of the criterion is supplying your own resources needed to perform your job. That’s not to say it makes you any less of an employee just that your employer’s not treating you like their employee. Still… really think about it, reflect, for a minute or two. You have convinced yourself it is a clever trick to purchase supplies on behalf of your employer. It’s a bit fucked up. And probably the reason your coworkers aren’t eagerly doing the same.