The second N in “environment” is seldom pronounced distinctly, 
so it’s not surprising that is often omitted in writing. 

Quiz     How earth-friendly are you


He goes for a picnic. (wrong)

If you are talking about a place and the activity, you would probably say, "He went ON a picnic."

"Went on a picnic" has 2,030 examples on Google, like these:

The last time I went on a picnic, I brought delicious sandwiches. As I read page 5, I remembered those sandwiches and this helped me read the ...


Yesterday, we went on a picnic. This has been our 5th (if you count the Sunday before where we ate picnic food at the house, but simply picniced ...

www.annecuisine.com/picnic_fare/index.html -

You might also say, he went TO a picnic if you think of the picnic like a party; you are going to an event that someone or some organization has organized.

"Went to a picnic" has 1,340 examples on Google, like these:

On Mother's Day we went to a picnic at Mission Bay. The clown had a parachute we could play in. I thought it wasn't fair that only three and four year olds ...


We went to a picnic that Steve had told me about given by a Community Group. It was a rather pretty town, and a nice drive (several hours from Conway). ...

"Went for a picnic" also exists. There are 1,210 examples on Google. "Went for," however, carries the meaning of "went for the purpose of," or "went in order to have," as in these examples from Google:

Yesterday, by way of a change, we went for a picnic to the shores of the Baltic, ice-bound at this season, and utterly desolate at our nearest point. ...

www.thefreelibrary.com/bs.asp?ss=text&s=picnic -

After lessons, we went for a picnic at a beach. It was pretty. We saw surfing. I go surfing tomorrow. Day 8: Today it was cold and I went to learn to surf. ..
www.infohub.com/forums/showthread.php?t=3822 -

"Go ON a picnic," is the most usual, and it means just to have a picnic. This might be a small family picnic. "Go to a picnic" means that you are going to an event, maybe a large, organized family picnic. "Go for a picnic" means that you are going for the purpose of having a picnic.
Poem Irregular Verbs

Как постичь глаголов ряд,
Ведь не все, как shut-shut-shut,

Hit-hit-hit и cut-cut-cut?

Не об стену ж beat-beat-beaten,
Лучше в рифму write-wrote-written.
Wake-woke-woken up, с утра
Разболелась голова.
Feel-felt-felt температуру,
Take-took-taken my микстуру.
Пол в квартире sweep-swept-swept, 
В чистоте всё keep-kept-kept,
На досуге dream-dreamt-dreamt:
Как удачу б catch-caught-caught,
На Карибы get-got-got.
Всю работу б do-did-done,
Чтоб на остров run-ran-run,
Или лучше fly-flew-flown,
Если путь не know-knew-known.
О финансах think-thought-thought,
Пару акций sell-sold-sold.
К турагенту drive-drove-driven,
Тот советы give-gave-given,
Мне в деталях tell-told-told.
Я дыханье held-hold-hold.
Он задорно speak-spoke-spoken,
Глобус чуть не break-broke-broken.
Я терпенье lose-lost-lost:
Сколько ж это cost-cost-cost?
За услуги pay-paid-paid,
Дома завтрак make-made-made,
С аппетитом eat-ate-eaten,
SMS-ки write-wrote-written.
На машине go-went-gone,
Путь begin-began-begun.
Дом счастливо leave-left-left,
В самолете sleep-slept-slept.
На Карибы come-came-come,
Родственникам ring-rang-rung.
Солнце в небе shine-shone-shone,
Ветер тихо blow-blew-blown.
В океане swim-swam-swum,
От туземцев run-ran-run,
Get-got-got в апартаменты,
Lose-lost-lost все документы.
Ногу чем-то hurt-hurt-hurt,
Прозу жизни learn-learnt-learnt.
Рану bind-bound-bound,
Паспорт find-found-found.
Жизнь сюрпризы bring-brought-brought,
Оптимизму teach-taught-taught.
Днем я даже read-read-read,
Новых people meet-met-met.
С ними время spend-spent-spent,
Деньги смело lend-lent-lent.
Время лихо speed-sped-sped,
К happy end-у lead-led-led.
«Отдых супер have-had-had»,
На работе say-said-said.
Всем подарки bring-brought-brought,
Пару акций buy-bought-bought.
В общем, жизнь – в обычный ход.