DS was very bored in kindergarten. One thing I did for him was at some point get him an ixl.com subscription. I think that a bright child who likes math can often self-teach a lot of basic arithmetic; something like this might work if your son is like that. DS liked ixl.com because it let him skip around at will, including into any grade he wished. I don't have a high opinion of another math site, xtramath.org, but you could check that one out too. (ETA: Many people also like ALEKS, and it's certainly better than a bare-bones drill site like xtramath.)
Another thing to keep him engaged might be to try khanacademy.org, watchknowlearn.org, and similar video sites.
You could also branch out a bit from math and begin getting him into things scientific, mechanical and electrical. Some ideas include science tools (microscopes, telescopes etc.),
workbooks,
models,
kits,
websites,
games, etc.; engineering-specific
kits and
lessons; and robotics / electronics / programming
toys,
environments or
training programs.
For reading I would just buy him plenty of interesting things to read, and spend time discussing what he reads with him. You might be able to get permission to send up-level things to school for him to read instead of being bored during reading time. And then, of course, you can always begin advocacy now for acceleration.
ETA: I guess one thing I left unsaid is that I would try to stimulate his interest, and go where it leads, more than anything at that age.
