I often make concentrated stevia-sweetened beverages such as lemonade and store them in the fridge in a mason jar,  diluting them with cold water and adding ice at the time of serving.
Try adding vanilla, orange, lemon, or peppermint extract to plain seltzer, or a touch of unsweetened cranberry juice.
I've taken some inspiration from these, usually without the added sweeteners:
 
A crock-pot is handy in two ways.  Either a night's dinner can be started in the morning, and left alone all day, or you can make large batches to eat several times during the week--or both!
 
Smoothies can be prepped in this way long in advance.
General directions:
Blend  everything except milk, water, and protein powder.  (This is usually 2 % Greek yogurt, frozen juice concentrate, spices, extracts, and any other seasonings.)  Freeze in 
silicon 1 oz.  ice cube trays.
For recipes with fruit, add 6 smoothie cubes, frozen fruit, chunked fresh or frozen banana (if included), and protein  powder in a zipper  bag.
For recipes without fruit, 8-12 cubes will be needed, enough that with the liquid it makes a 16 oz. smoothie.
Freeze.  Empty the bag  into a blender.  Add the indicated volume of liquid plus and 50-100% more depending on the strength of the blender, and how thick or thin you desire the smoothie.  This will usually yield frozen yogurt / soft  serve you have to eat  with a spoon!  Let the  smoothie pack contents  thaw before blending if  you have an older  blender, or want a less  thick smoothie.  
Adding  the protein powder  thickens and "bulks" the  smoothie and I haven't  measured how it changes  the volume in my DIY  smoothie cubes.  
 I've not tried it, but others have had success with 
blending and freezing smoothies in advance, then thawing them in the fridge the night before.
 
Having a number of dressings and sauces on hand makes it easier to prepare meat one way and make several types of dishes for variety, particularly with pan-grilled chicken on salads.  Using 1/2 T. each sunflower oil and butter, liberally sprinkle a hot skillet with salt and fresh cracked pepper, then quickly add boneless, skinless chicken breasts, or lean boneless steak, and pan-grill the meat.  5-6 minutes per side for chicken, and 4-5 minutes per side, depending on thickness, should yield medium-rare steak.  Let the meat rest and slice cross-grain 1/4" thick.  On a bed of mixed baby greens, layer a few varieties of diced or sliced vegetables that complement the sauce, add the sliced meat, and drizzle with the sauce or dressing.
Other sauces and dips, such as hummus,  can be prepared in advance and make a quick snack with a few chopped vegetables.
 
• Freezer Meals •
Some of these dishes lend themselves to being frozen after cooking.   It works best with partially liquid meals with small pieces of  ingredients, such as chili, thicker soups and stews, pulled pork or chicken dressed with barbecue sauce, burrito bowl filling, etc.
Fill a gallon zipper bag with enough food so that it is about 1/2" thick when lying flat on it's side, maybe 1/3 to 1/2 full.  Squeeze out all the air as you seal it.  Lay flat to freeze.  Frozen in this way, with this thickness, it's relatively easy to gently bend the frozen bag of food and break it into individual portions, to remove only as many as desired for reheating.  If the food is very thick, you can used a chopstick to press portioning grids into it from the outside of the bag.  You might also try this with partially frozen meals.
 
• Freezer Prep •
Once I have reasonable freezer space, I intend to 
freezer meal prep for crock-pots.  
 
I   make four days' worth of the same variety in one large glass snap-lock   storage dish.  Four days' breakfast made in under 15 minutes, no  cooking  involved.  Some make individual portions so you can choose among several varieties.
 
A pressure cooker can be a quick alternative to preparing dinner in the evening, if you don't have or forgot to use a crock-pot.  Again, you can make large batches, and 
eat a dish several times in a week.
 
Salads can be 
packed ahead of time in jars or other containers.  The order of layering is important to keep ingredients from turning slimy.  I have many excess jars, but I need to remember to bring a vessel from which to eat the salads, such as a large bowl, as it's incredibly difficult to eat one from a jar.
 
 
I often portion soups into canning jars (it's important to use canning jars and not mayonnaise or pickle jars, or other glass vessels not intended to handle high heat).  These I reheat, lidless, in the microwave.  Handle with care as the glass will get hot as well.
If you leave enough headspace, and leave the rings or lids loose, you can freeze the soup in the jar.  (Headspace is an air gap at the top, the space depends on the total volume of the jar.  Usually 1/2-1" is sufficient.)  Once frozen, tighten the rings or lids to prevent freezer burn and for safe storage as the liquid thaws.  These can either be left to thaw in the refrigerator, or gently thawed in a pan of a small amount of warm water, set on low.  If uncertain about any of these directions, please search the internet for more details before attempting any of these methods.