Make the table into a shipping container -- problem solved
The rules don't specify where the line is between "an object" and "not an object." Frankly, that's a good thing. This alleged imprecision gives both the DM and players room to work, to be creative, or to be imaginative. (Or, to not worry about it if that level of granularity / simulation / pedantry isn't where the players at the table gets their fun)
To solve your specific problem (a table loaded with loot)
How about a 10' long table stacked with gear? Is the table also a container in the same way or would teleporting a table not teleport the tablecloth?
From the spell description: (SRD, p. 183)
This spell instantly transports ... a single object that you can see within range, to a destination you select. If you target an object, it must be able to fit entirely inside a 10-foot cube, and it can’t be held or carried by an unwilling creature.
Turn the table upside down, pile the stuff on the bottom of the
table. The legs define the four corners of a container.
Cover the pile of stuff/loot with the table cloth (and if needed, capes/blankets, etc).
Using the 50' of rope that one of your party carries, and adding a shield
on each long side of the table to stiffen and give shape to this
pile, strap it all down. As necessary, use ten-foot poles1 to support the top of the two long sides further. Viola! You have one object: an improvised shipping container.
Teleport it to your selected destination (to save on postage2).
A weight limit (if you want one)
The weight limit can be estimated in a variety of ways. The rules give room to work, and D&D 5e is "rulings over rules" in intent.
This spell instantly transports you and up to eight willing creatures of your choice that you can see within range
Whatever you and eight people like you weigh and can carry, based on the 15 x STR carrying capacity. (SRD pp. 79-80. Same as Basic Rules).
Lifting and Carrying
Your Strength score determines the amount of weight you can bear. The following terms define what you can lift or carry. Carrying Capacity. Your carrying capacity is your Strength score multiplied by 15. This is the weight (in pounds) that you can carry, which is high enough that most characters don’t usually have to worry about it.
Push, Drag, or Lift.
You can push, drag, or lift a weight in pounds up to twice your carrying capacity (or 30 times your Strength score). While pushing or dragging weight in excess of your carrying capacity, your speed drops to 5 feet.
While the limit would vary depending on each creature's STR score, you can use an average for your ruling. If you use 11 STR as average, then 165 x 9 for 9 human sized creatures. Add the weight of 9 human sized creatures themselves. For ease of calculation we'll say each weighs 165 pounds (sans gear).
165 x 18 = 2970 pounds or just under a ton and a half.
Substitute in different values for average load on a creature and average weight, and you'll get a different max weight, but that's your ballpark figure if you want to define a weight limit. Since movement isn't an issue here, using the 30 x STR (encumbered) would make some sense, so the above would be 165 x 27 for 4455 pounds: about two and a quarter tons.
Liberal estimate that pushes RAW a bit
Whatever you and eight creatures that you can fit within a 10' radius circle weigh and can carry, per above. (8 horses? 8 oxen?) The limit there is how big a creature you think you can pack into that area, what it's STR score is, and thus what it can carry. Play around with creatures until you get a number you like.
1 Iconic dungeoneering gear. What do you mean you didn't bring a ten-foot pole? You're playing D&D, right?
2 Side effect: FedEx and UPS share prices on the Waterdeep Stock Exchange drop a bit in response to your brilliant problem solving. Agents form Aurora's Whole Realms Catalog contact you about trade rights infringement, through their solicitors.