You would need to check what the "rules" are for the event.
Commercial vendors may be "protected" and you may not be allowed to sell specific items.
Similarly, be careful you are not breaching any copyright matters.
Some of the Guilds around here sell remnants (pre-measured) donated by their members.
Or make up pre-cuts ... layer cake, jelly rolls, charm squares etc.
Likewise, kits could be made of fabrics and patterns.
Also, used quilt patterns, books and magazines are often out and waiting.