Hmmmm, what kind of things? You can buy plenty of annuals in bloom, hundreds of little pots with little blooms sitting around for people to kick or trip over. You could but large pots of tropical hibiscus but they might not decide to bloom the da of the party. I think you need to buy plants a few days ahead of the party and plant them. That is the only way to be sure you have the results you want.

for shrubs, try roses and/or hydrangeas.
also, there are a few late-blooming azaleas that could fit the bill for that time-frame such as 'macrantha' and 'gumpo'.
a plethora of perennials are out there to choose from as well as the annuals that terry mentions.

nanny, there are countless annuals and perennials that will be available for planting at this time of year. Countless! I wouldn't wait until just a few days before the party though. If you get some annuals in now, they will have had time to grow nicely. Should you select some perennials, go for those with a long bloom period. Some of perennial Saliva come to mind. I bought some in full bloom last year, and enjoyed them for months.

Of course, lusious containers bursting with a mixture of colorful flowes and stunning foliage comes to mind, too.

The Knock Out roses would be sure to be a hit, too.

Truly, what a fun project! I'd hit those garden centers soon, though.