Table and bench 120 lbs.

A-frame table (Tank Model) 180-250 lbs.

A plastic table will be around 80 lbs.
Commercial-grade metal picnic tables can be the most durable and weigh between 220 and upwards of 500 pounds.

My Design (Jeep model - Small, maneuverable, light but sturdy, functional):
I salvaged the redwood top of an a 40 year old A-frame table and after plaining it down, sanding it and filling knot holes with epoxy reused it to make a new tabletop.
Now I needed to figure out what to do about legs.

I looked at dozens of designs on the internet. Lots of handymen published their ingenious designs, some of which were very creative.
But many seemed more to show off the woodworking skills of the designer than usability. I didn't see any that met my objectives, so I tried my minimal creative skills to design one myself.

I had several objectives :
1. Make it lighter and more portable.
I initially thought of foldable leggs, but those wimpy card table leggs did not meet my aesthetic requirements or sturdiness.
Real wood leggs the were foldable provided challenges too. 2. Provide more legroom so you can sit at the ends and
Having a 4-2 configuration (4 on the sides and 2 on the ends) rather 3-3 design (3 on each side) provides more community. You can see everyone without bending forward. 3. Lower it so it would work with my 16" lawn chairs and a standard 18" chair and be more friendly for my 3 1/2 year old grandson. I did this with low profile bracing underneath providing sufficient support to avoid leg collapse, but enough legroom for anyone but a sumo wrestler.
I wanted to eliminate the skirt around the edge in most dining room tables, so it would accomodate an 250 pound 6 footer while being lower.

4. I wanted to make it stronger than the model above.
The problem was to provide leg support so if a 200 pound person fell into it or someone tried to drag it across the yard the legs would not collapse.
There can be a lot of torque trying to break the legs loose in those situations.

I did this 2 ways:
1. Putting rollers on the legs so it would move without friction in those situations -- fall or draging.
2. Designing a low profile bracing system allowing more legroom using aluminum angle rods and an 2x4's between the legs right under the cross pieces holding the top and bolting the legs to the top cross pieces.

I made 2 17" high benches for the sides.

Here's what I came up with:
The table is 46 lbs (so I can lift it with my 75 year old back) and the benches are 37 lbs each for a total of 120 ;bs instead of the 200-300# of an A-frame table lbs.

An outdoor workbench with piece of 3/4" plywood with a vice and grinder which can be attached to my garage bench or this table.

Sample Dimensions:

What      Table Chairs
Cabin Deck  32" 20.5"
Davis 
Dining room 32  18
Front           17
Lawn Chairs     16

Links:
5 Tips For Using Epoxy to Fill Cracks & Knots in Wood
The Rustic Outdoor 24 Table