I use a Korg Pandora Acoustic Toneworks which is small enough to mount on my guitar/instrument straps. It does a big range of useful things and is programmable with 50 user combinations of many types of effects. The sound quality is good and noise is low.
On the strength of this little device I've sold several Boss pedals is used to use and which were a nuisance to to carry around. The Acoustic Toneworks fits in my guitar case.