This would be an EXCELLENT time for you to invest in a boom box. Hopefully you negotiated a good price for this job and it will help you pay for a usable boombox that you can cart to gigs.
You have two options.
You can put in your contracts that the client must provide a sound system (which can be VERY risky...as they might decide that a small child's cd player will suffice and could very well not even play your cds!!!) OR you can purchase a good boombox that will be good for home-based parties or small venues where there are 50 or so guests.
I used to carry a very efficent boombox...I used it for class, gigs...but it wasn't loud enough...so...about 2 years ago I finally upgraded to a massive boombox...it's the Sony ZS-H10CP CD Boombox
Amazon.com: Sony ZS-H10CP Heavy-Duty CD Radio Boombox: Electronics
It is LOUD, not horrifically heavy, (challenging to sneak into jobs where you're the 'surprise' for the GOH, but still do-able!) and has a great control for sound, bass, outputs for mic and iPod (which I use often!!!) as well as CDs of course. And it's under $200 (this link from Amazon has it at $117 I think with shipping a bit more...I found it at my local electronics store and didn't have to pay near as much). Runs on battery as well as AC.
Gia