I always prefer my tanks to have plenty of stowage. Even German tanks, which were normally far less heavily stowed than Allied vehicles, look better with some helmets, water bottles and jerricans hanging off them. Until Rubicon put out some plastic accessories of their own, it's necessary to find other sources. From what I've been able to find out, it seems to be a fairly limited choice.
The only dedicated 1/56 scale accessories are produced by Warlord and Die Waffenkammer. Warlord's are metal, and Die Waffenkammer's are resin. I'm not keen on attaching lots of metal to my plastic tanks, so I'd rather go with the resin. I'm not sure about the quality of Die Waffenkammer though - the photos of the accessories sets on their site aren't very clear, and the painted examples on the web look a bit misshapen. Has anyone had any experience of these?
Tamiya produces a reasonable range of plastic accessories in 1/48 scale, and I've found that many of these work quite well - my Rubicon M4A3's now have a lot of stowage courtesy of Tamiya. It's slightly over scale, but it doesn't matter when it comes to bedrolls and generic boxes. It doesn't work so well when it comes to jerricans, spare wheels, spare tracks and ammo boxes, because they are obviously too big (just compare the 1/56 scale jerricans in the Warlord SdKfz 251 kit with the 1/48 scale Tamiya version). Helmets and packs are okay, because they tend to be over scale on 28mm minis anyway.
Black Dog, a Czech company, do a range of beautifully sculpted resin accessories which are designed to fit Tamiya kits. Unfortunately, they're also therefore 1/48 scale, and probably difficult to adapt to 1/56 scale.
You can also use Tamiya 1/48 scale figures to crew your 1/56 scale tanks, although you need to be selective. 28mm minis tend to have 'heroic' proportions, with oversized heads and hands, and shortened legs; Tamiya figures more naturally proportioned (although they have always been rather too slender looking). Tamiya figures look okay if you remove the legs, which is fine if they're sitting in hatches. They will probably look better if you replace the heads and arms (assuming they're going to be fielded with Warlord minis). Tamiya's British tank crew are especially nice - you get enough on one sprue to crew a few vehicles.
Have I missed anything? Anyone got any other thoughts or preferences?