Based on the additional comment you gave, I would recommend that you keep the capital from the businesses separate as much as possible.
It sounds like you won't get into any trouble legally if you make 'loans' or transfers of capital from one business into the other. But I would suggest that you keep detailed records of any transfers that you do make.
The reason why is that in any business, it is important to know the economics of how your business makes money. If you find yourself making transfers repeatedly, then your business model may be bad. Even if your transfers are only to deal with the cost of poor customers, it could still mean that your business model needs to be adjusted.
But if it's a question of the timing of cash flows, then there's really nothing wrong with taking some of the money from your successful pants operation and building up more working capital in your stationery shop.