Looking for a way to improve at delivering compelling table topic speeches? Try a writing prompt notebook like this one from Piccadilly. Each lined page has 1-2 brief prompts along the lines of what you might expect to encounter in a table topics session during a Toastmasters meeting. Flip through, pick a prompt (or throw literary caution to the wind and select one randomly) then write out a half to full page response. To ensure you focus on impromptu thinking, try not to pause during your writing (the process of writing already provides a built-in delay). And try to resist the urge to wordsmith since this isn't something you're generally able to do when speaking extemporaneously.
This type of exercise is great because it's easily portable and can be done on your own, i.e. when you're jonesing for your next meeting, but it's still six days away!