You have gotten such great advice, I'm a little reluctant to "get my oar in" on your questions, littlekrb.
You seem to be asking, "After lettuce is gone, what will I use in my salads?"
I'm really not that much of a salad or even a raw veggie eater. Yes, I do enjoy a salad but, unlike Hendi_Alex can't really go some of the other things raw. So . . . I stir-fry.
Maybe not with Hendi_Alex's arugula but even its relative the radish is pretty darn good sliced up in a stir-fry. Kind of takes the place of water chestnuts
. Lettuce, too! My grandmother's "wilted lettuce" may have been my 1st introduction to the good stuff that can come out of a garden. You can also do that with lettuce that is just a little past its prime . . . or, let's just say "full grown."
If you think about it, whatever you are putting on a salad as a dressing, pretty much, can go into the skillet with the veggies in a stir fry. So, you have oil - start with that. A little shake of seasonings and/or minced herbs - some bacon bits, maybe. Splash on a little vinegar - you are done!
Taking this direction, you can grow things like bok choy a little later in the season than lettuce. Even as the bok choy begins to flower, those flower buds and the stalks are usually nice & sweet. Of course, broccoli is much the same thing. There's one that I like to grow that can get big and make nice flower buds - Senposai. It even seems to run later & can take more heat than the broccoli.
Of course, beets/chard/that family including something called Perpetual Spinach, can be cooked in a skillet or wok. Probably my favorite veggies are the little, baby beets. Even tiny thinnings from the beet row are tasty.
Like Applestar, I mix my plantings - calling it a "salad bed" no matter how I'm using the plants. I use succession plantings as do your other responders but like JAL_ut, I don't have a whole lot of time for that. Still, that July 4th deadline
is quite a ways off and I'm always poised to get the seed for more salad greens in the ground by the end of August. It's greenbeans and summer squash by July 4th and, not just lettuce but more of the small varieties of bok choy & other Asian greens after the August heat.
Cucumbers? You can just cut off that shriveled tip after harvest or remove the fruits that don't look like they are developing properly. In a short time, you will have more cukes taking their place and, hopefully, developing properly. They like a lot of water which kind of sets them apart from some of the others in that family. Best of Luck!
We are each other's harvest; we are each other's business; we are each other's magnitude and bond. ~ Gwendolyn Brooks