Here are some double-barreled words that have come up:
atsu-atsu: hot/piquant food, hot lovers
bao-bao: from Chinese: good.
botsu-botsu: pimply, like a rash.
bu-bu: the sound a pig makes.
dai-dai: Seville orange
doki-doki: my heart is pumping with excitement!
don-don: big amount
fawa-fawa: squishy, soft like a cloud.
gari-gari: hard and crunchy like ice.
hoku-hoku: with the taste of a hot chestnut or sweet potato.
ji-ji: very old, grampa.
kata-kata: chattering teeth.
mochi-mochi: texture of a dumpling
nya-nya: the sound a cat makes
paku-paku: eating like the mouth of a fish
shaki-shaki: fresh, crunchy vegetable texture, jerky movement
soro-soro: shall we? Said when trying to get a group to go somewhere.
sube-sube: smooth like an eggshell
wan-wan: the sound a dog makes