How small of an item? Maybe an ultrasonic cleaner would work? Ultrasonic cleaners are portable and have a self-contained reservoir. The process takes a while, but it's very low effort. Also, the cavitation effect (the method by which ultrasound actually cleans surfaces) works on small nooks and crannies (though I can't recommend that you try to clean a Thomas' English Muffin) and also on the inside of surfaces that are otherwise inaccessible.
I suppose a power washer would work for somewhat larger objects with broad angles. Amazon has a few small units, like this one and this one. I don't think any of them have self-contained resinous because the high flow rate would make this impractical. If you assume a 1.5 GPM flow rate, and you wanted to use the washer for 10 minutes, you'd need a 15 gallon reservoir, which would weigh 125lbs for the water alone. A more realistic 2.0GPM flow rate used for 30 minutes would require a reservoir weighing 500lbs.
Thinking in terms of a high-pressure spray bottle. Would it be possible to build a device to shoot out a high-pressure spray from a small reservoir? Possible parts: small paint spay pump combined with a special nozzle.