How to prepare vegetables for a sandwich that can last for several days in a fridge? I'm not much of a cook but neither am I a complete stranger to the kitchen. I like to prepare sandwiches to take with me to work in a box. Since I do it often, I like to make them more "interesting" than just plain bread-meat-cheese. So far however I've only come up with the idea of putting in various off-the-shelf sauces/dressings/whathaveyou that I can buy in the supermarket.

Whenever I buy and eat pre-made sandwiches, they taste a lot better than what I make myself. I've tried to figure out why this is and I think it's because they contain vegetables. I like vegetables in a sandwich - cucumbers, lettuce, tomato, avocado, bell peppers, etc.

The problem with adding them myself is that it just takes too much time to do. I usually make the sandwiches in a hurry in the morning, so I have about 5-10 minutes to do it. Washing-peeling-slicing-storing - that just takes too much time. Sometimes I add pickles, but most of the time I consider even that too big of a hassle.

So I was thinking - if I could pre-slice the vegetables and store them for several days (ideally - up to 5 days), that would do it. I'd just have to grab them from a box and throw them on the sandwich. I'm afraid however that sliced vegetables won't keep so long, even in the fridge. I haven't tried it though.

Are there any tricks out there that could help me? Some way to make sure they last longer, or perhaps are much quicker to prepare in the mornings? We can skip tomatoes, I think a sandwich with tomatoes in it would be a mess after several hours in a box anyway.

Or perhaps other ideas to quickly give a sandwich an interesting taste? (Subjective, I know, but I'm not picky and will try different things)
There’s a third option between storing the vegetables for a week and cutting them in the morning:

Cut just the amount you need for one morning the evening before. Storing overnight is not a safety issue (assuming basic principles like storing in the fridge are followed), and you still can “slap them on” as requested.

Another thought:
You describe cutting in the morning as too time-consuming, but my favorite tool in this context is a small cheapo vegetable slicer (like this one). I hold it right over the sandwich, shave a few slices of cucumber or similar right on it and am done. Thirty seconds, tops, including a quick rinse.

If you are interested in other toppings, I suggest you take a second look at the leftovers from yesterday’s dinner: Leafy greens like lettuce (sans dressing!) keep well for a few days and some roasted vegetables are also interesting: Either they are already spiced or a dash of lemon or mild vinegar plus an overnight stint in the fridge gives you a perfect sandwich vegetable - not unlike antipasti. Slice them right when you are packing them up, of course, for a grab-and-go sandwich preparation.