A few things of note in terms of healthiness.
Generally, eating your 3 meals and no snacks is better than eating a lot of snacks, and that is better than eating 3 meals and a lot of snacks. Unless you're always under-eating, but still.
The time of day will dictate what you should bring. If it is in the evening, bring light foods. Lunch or breakfast, heavier things. Eating heavily before you go to bed is the wrong way to lose weight. You consume all your food and calories... Then go to sleep. You're better off having the heavy meals during the day to provide energy for activities, and use those activities to burn the calories.
Exercise is also a VERY important factor that cannot be underestimated. My mother is obese, and has been dieting for... God knows how long now. At least 5 years. She has barely lost any weight. The reason for this is she wakes up, drives to work, works, drives home, then eats and goes to sleep. I, on the other hand, eat a fair bit, but also walk on average 10,000 steps per day, alongside other bits of exercise weekly, which ends up making it very difficult for me to actually put on weight. I started to for a while, but now I'm back to losing it again.
All this in mind, I wouldn't do snacks. I'd take a break for a meal, and eat appropriately. Tradition or no, your friends are dieting and trying to lose weight. You're already breaking the tradition by taking diabeetus bait out of it, may as well go the whole hog. If there are no snacks, there are no temptations. They can't be tempted into eating too much. If that's not an option, plenty of other suggestions in the thread.
With snacks, if possible, I'd try to theme them around what you'll find in the game, and encourage eating them only when you acquire them, and that eating them decreasing your stash of them. So you could find/buy some grapes in the game. This allows you to eat grapes. If you eat the grapes, however, your character no longer has the grapes. Helps immersion, can be a bit of fun, and helps limit how much each person will eat, or pace it. This will require co-operation of the DM if you are not the DM.
Additionally, try and work physical activity into the run as much as possible. I've had DMs that have had us all get up and act, had us actually write poems and then judge us on them to see if we woo the lady or not, and, where appropriate, have us perform other IRL feats in substitute of our characters. Its fun, entertaining, and so long as its worked into the game well - balanced and enjoyable. It also gets people up and doing a bit of exercise. The focus naturally still has to be on your stats and your character's skills, however rewarding good shows IRL with a +1 or +2 to a dice roll, and encouraging players to try when they're 1 or 2 short of what they need can work. More often, its better to get a skill that isn't related to what the characters know - something like dancing, which may be in the rules for a role, but its probably niche enough that most people wouldn't know about it - and make the players perform it IRL in order to pass, instead of making up a roll to work for it. Again though, requires co-operation of the DM.
Honestly, the best thing you can do is try and work things into the scenario. It turns the diet into a game, and makes it enjoyable and fun for everyone, whilst also helping with the goals of weightloss. Its not always easy to do, and I know its not exactly addressing the OP, but if you want to go to that bit of extra effort, its something to consider.