Perhaps as simple as setting a chair or TV tray/table to the side of where you are sitting, with your supplies atop? Sitting them on a tray makes it easy to remove, and keep all in place, when /if the chair is needed elsewhere.
Depending on how much and what stuff you want to keep close at hand, you could could take BearIsGray's idea of a walker bag, converting it to hang over the chair back, so it hangs directly above the things on the seat. Or if using a TV tray/table you could have the converted bag hand in front.