Disclaimer: This is for Type 2 diabetes. Type 1 diabetics take insulin and can adjust their insulin dosages so they can eat things I cannot. I already have insulin, but my body can't use it, so I take meds and change my diet to make it easier for my body to process that insulin.
If I was providing a Continental breakfast, I'd include boiled eggs and regular/steel cut oatmeal. Nothing in it. I'd make available butter and/or milk to accompany it. Many Continental breakfasts do include fruit already, but too much fruit is bad for me, too. (Some fruit is okay. Also, some fruit, I have to avoid totally.)
For snacks, I'd make sure there was some fruit and some nuts and some cheese. Not all sweets and junk.
For lunches and dinners, I'd make sure there were options that included wheat/rye bread if sandwiches were provided. I'd make sure there was salad as an option instead of chips/fries.
For restaurant meals, if each individual orders and pays for their own, there is generally NO problem. I can exchange a potato for additional veggies most places.
If there's pasta of any sort, I can't eat it unless it's wheat. I'd never ask someone to make that kind of change, but it would be nice if there's at least salad included in a pasta meal. That, I can eat.
I just avoid deserts altogether. When I'm home, I provide for sugar free/no sugar added items if I want them, but when I'm out, I just avoid altogether. It doesn't bother me until people start questioning me about why I'm not having desert. :)
PLEASE NOTE: I am not suggesting that writing workshops or retreats should actually do the above. I'm just speculating about what I'd do if I was in charge of something like that...just so folks can see that it's NOT a huge deal accommodating diabetics. Most people just don't think about it, I guess.
If I'm able to prepare food and have easy access to a grocery store, I can prepare my own. Easy is the key word. Many workshops and retreats are in off season and are some distance from stores and restaurants.
I will definitely pack nuts for the upcoming writing retreat, but I can't pack anything that would spoil and I'm not going to have the ability to prepare my own food.
It's just something I think about when I travel. Not to be a pain in the ass, but because I have to.
EDITED TO ADD: I do realize that many hotels have a set catering menu for breakfasts and lunches provided for a group. In that case (and I realize organizers most likely can't do anything about this), it would be nice if the hotels didn't ban outside food from being brought into their venue.