The most significant feature of modern banks is fractional-reserve lending. Your bank borrows $100 from you (e.g. by letting you deposit money in it), lends $90 to your neighbor, and predicts that by the time you want your $100 back, someone else will have paid off its loan so that the bank has $100 in liquid cash sitting around. (If that prediction turns out to be false, then your bank borrows money from another bank, and if no other bank is willing to lend to it, then the government steps in.)

There's no way you can play this game without a large amount of money and a willingness to jump through the government's regulatory hoops.