I've been riding my Tricross Comp for about a year now. I mostly use it to commute to work (20 miles round trip, 4 days/week) but I've recently started to use it more for grocery shopping and other errands. I can offer some suggestions on accessories that have worked out well for me over the last year.

As others have noted, the secondary brake levers leave you with a very limited amount of handlebar to work with for mounting lights, GPS, etc. The $15 Topeak Bar Extender worked out really well for me. It allowed me to get my Planet Bike Alias HID up higher (to clear the cables) and get my GPS (Garmin Edge 205) up higher where I can see it better.

I initially used a cheap rear rack from Performance, but recently replaced it with the sturdier Old Man Mountain Red Rock rack. It's considerably more solid and has a 60 pound weight capacity. Its longer and attaches to the brake bosses, allowing it to sit farther back pretty much eliminating any problems with heel strike.

I use an Arkel Commuter pannier (plus rain cover) for commuting. It has a removable, padded laptop compartment and a really nice attachment system. I use a pair of Nashbar Townie baskets for grocery shopping and miscellaneous errands. It's nice that you can fold them flat and that they come with their own rain covers.

I used SKS P35 fenders for quite a while, but kept having problems with toe overlap (hitting the fender with my feet while turning and pedaling). I replaced them with some Planet Bike clip-ons which have worked out well for me. They also look a little better on the Tricross, IMHO, than full fenders.

My latest addition was an Airzound horn. It didn't mount easily - I had to zip-tie it around the Tricross' oversized handlebars, but I was able to get it in a good position. While I don't use it everyday, it comes in handy when I need to get someone's attention. I left the bell on as well to get the attention of fellow cyclists and the occasional pedestrian.

Overall, I can't say enough good things about the Tricross. It's an amazingly versatile bike. I can take it grocery shopping, ride through gravel, up steep grassy hills and easily keep up with my road bike riding friends on the weekends. In 2,500 miles of riding, I've yet to have a flat. I occasionally wish it had a triple rather than a double crank, but I have plenty of gear ratio choices most of the time.