For those with sticky out embellishment I do provide a thicker stronger envelope.
My envelopes are a bit thicker and big enought to take the flowers etc
I usually have my cards in cellophane bags and then fold the printed receipt around them. If I have cards with flowers or other large embellishments on, I wrap them in bubble wrap before putting them in the envelope.
I generally use recycled envelopes (the ones that you get DVDs and games in from a certain large online retailer). It keeps my OH happy as I actively encourage him to buy films and games so I can have the envelopes. 
All our cards are in cello bags, then I put them in a paper bag with a business card and thank you note, I use one of my stickers with website on to stick it down. Then that goes into a card board backed envelope with Do not Bend on (I pick these up for 18p each on line), then I have just had a stamp made with one of Markās sketches and website address so I stamp this over the envelope seal and put a bit of cello tape across to secure it. (hopefully the post man might be intrigued enough to check out the website then - after all companies like Amazon are plastered all over their packaging!).
I would like to use recycled packaging (and did when I first started) but I prefer to use new. I then use all my old envelopes etc to transport my mosaics in when I am doing shows, that way I can ask the customer in person if she/he doesnāt mind it in recycled packaging, most of the time thatās fine.
All my cards are flat, so I dont have to worry about embellishments etc.