Now assuming you got yourself a tunic or a tabard, which you should've gotten by now(seriously a tabard is a rectangle of canvas with a hole for the head), you still got a few things to do before calling your first basic garb done. Modern shoes and jeans are one of the things people don't often deal with, for one reason or another. Its sad, because its rather easy to do something about it.
Not everyone back in the day was a noble, a warrior or a merchant and a good pair of boots wasn't easy to find and was quite expensive too. There is a reason after all why boots were one of the first items looted from the battlefield. The most common people were(wait for it....) commoners. No kidding Sherlock! Well playing a peasant is hardly fun but that doesn't mean we can't borrow a few ideas. The simplest of them - feet wraps.
They were quite common you know, and all you need to make them is some canvas and laces. You could turn them into a part of your costume, or you just use them temporarily if you have nothing better.
Material - canvas - two strips roughly 1, 1.5 meters long by 20-30sm wide. Laces.
You don't need tools except a scissors/knife to cut the canvas...
How exactly you use them depends on what you plan. For example if you have acceptable heavy shoes and want to cover your modern pants - you will wrap them around your shin and tie them with the laces.
If you have the time you can make them rather good.
If the bigger problem is too obvious sneakers, and you have a way of covering your shins, then we go the other way around.
Yeah they won't exactly fit on my character would they?
So we bind them with the canvas and tie them with the laces.