> it shows there being a speaker present, but don't I need to know what watt and resitance the speaker needs to be?
Bah. Only wimps and technicians worry about "power rating" and "impedance". Real players just play. If something smokes, it was no darn good to begin with, right?
Speaking as a wimp and technician: I think a LM386 on 9V supply is good for about a half-Watt at most. With a solid 9V supply, maybe a whole Watt of gross distortion, on a 9V battery you won't be able to hold even the half-Watt long enough to melt a small speaker. Yes, if you really shop around, you can find "loudspeakers" that can be melted with 1/10 Watt; if you just grab a kitchen radio from the second-hand thrift-shop, its speaker will take everything the LM386 can dish out.
Impedance? Well, the LM386 will distort more at medium level with 4Ω than with 16Ω, but at full-blast it is all about the same.
Oh: a half or whole Watt may seem like it would be lame next to your 80W big-amp, but you can make a heck of a racket with a part-Watt and a good speaker.
Oh: put this little amp into a twin-twelve cabinet and it will make a very gutsy racket yet not at such volume that you wake people two streets over. That does not fit your definition of "portable", I suppose, but do try it with a big speaker. A fairly large speaker, like a screaming-Six, in a large but lightweight (corrugated cardboard, or 3mm plywood) box will make the most of a minimal amplifier.
> it's a guitar amp so it has to have tubes.
Agree, but: tubes are such power-pigs that battery or ultra-compact construction just isn't happening. When location is more important than tone, you can make a nice noise with an FET/386 amp and a 9V battery, and play anywhere.