Accompaniments for smoked trout (individual picnic lunch)

I would put some lemon, capers, fresh thyme, and thinly sliced onions on top of the trout. And pair it with an arugula salad with a vinaigrette made of hazelnut oil, olive oil, balsamic vinegar, and champagne vinegar. In the salad I would put some thinly sliced onions as well. Hope this gives you some ideas :). Maybe some assorted berries with balsamic for dessert.

Fresh grated horseradish mixed with crème fraîche and a little cranberry jelly. Or no jelly.

Horseradish is smoked fish's buddy.

A lentil salad.
Vinaigrette based potato salad

I would serve it with potato salad with dill and horseradish and an apple and fennel slaw or maybe a fresh corn salad? The salads can be made the day before and last for a few days. I also really like blueberry crumb bars- they are sturdy and they pack very well.

shredded salad of carrot and radish with a dijon vinaigrette.

Water crackers
Pickles
Celery sticks
Tomato, onion, and cucumber salad, or maybe simply sliced tomatoes
Something with bubbles to cut through the rich trout - beer, sparkling wine, cider, or water

My first thought was a roast potato salad with a chili lemon chive caper vinaigrette.

I might also pack some water crackers and some cream cheese with some capers and chopped preserved lemon mixed in. I love this cheese mix atop crackers with some smoked fish atop.

Unconventional:
Make a savory yogurt bowl with plain greek yogurt mixed with shredded cucumber and chopped green onions, S&P. Top with cherry tomatoes, capers or olives, something crunchy like sliced almonds.
Add the trout to the top. Scoop and eat with sturdy plain pita chips (like stacey's naked flavor)
+1 for a bubbly beverage

I am seconding:
1) Crackers. Although you have probably already thought of that.
2) Vinaigrette potato salad. Something like one would make as part of a salade nicoise. I would use dill and parsley as my fresh herbs. I would actually use this as a jumping off point for my picnic and pack tomatoes, blanched or pickled green beans, hard boiled (or deviled?) eggs, lettuce leaves to make wraps... What can I say, I like a theme.
3) Bubbly beverage. As someone who has just been enjoying a late-night snack of stale crackers and smoked whitefish dip, smoked fish is persnickety with pairings. I like a strong Belgian beer with smoked fish, or a very crisp, tart bubbly wine or cider can also work. Non-alcoholic? Maybe a fizzy lemonade on the tart side (maybe with a little thyme)?

Mostly preferring to serve finger food at a picnic - I'd include a baguette, brie, a favorite white wine, green and black grapes and a couple squares of the finest chocolate your money can buy.

If you feel you need a 'veggie' then go with pickled beets, pickled onions, etc. - or caprese on a stick (cherry tomatoes, cubed moz and basil)

Enjoy your picnic!

Thanks, everyone. I'm picking and choosing different items from the responses, based on items I already have. I will eat the trout with capers, dill, and lemon slices. My sides will be a cucumber salad, berries dressed with balsamic, and a berry bar cookie. And a bottle of Perrier. I will bookmark this page and refer to it next time I buy smoked fish.

Tater salad, cream cheese and crackers.