If you are starting your own business, you likely have a significant amount of experience in your industry, or passion which is just as good. I found that a lot of skills I developed while starting new businesses are transferable and there is a demand for them in a freelance marketplace. I have been consulting on and off for pretty much my whole career, even when being neck deep in a new venture. I would suggest identifying a few skills which you can sell by offering them on part-time basis: writing, programming, SEO, creative design, etc. Utilize your network by offering your services or even use larger freelance marketplaces like UpWork. I do not think I would have been able to sustain myself without this kind of work while bootstrapping a new idea.