Did you just dunk a basket of hand cut fries into the oil then realize that you don't have any 'sauce american'? Well you could make a basil aioli or you could take 20 to 30 minutes to make a good catsup substitute from canned tomato paste.
Step 1: What You Need
Who are we kidding, if you've let yourself run out of a basic thing like ketchup, then you're not going to have tomato paste. But in the off chance you do, here's what you need to go with it:
12 oz tomato paste
1 1/4c distilled vinegar (I did a mix of distilled and white wine vinegar this time)
1 TB salt
1/2 tsp onion powder
1/2 tsp garlic powder
1/4 tsp red pepper
1/8 tsp allspice
Many, many options. Toss in whatever extras you want. Hot pepper powders, herbs, different vinegars, replace the water with beer or wine or bourbon. Do what you like.
Mix all of the ingredients together. Whip it up with a whisk and transfer it to a pot on your stove.
Step 2: Cook It
Bring up the mix to a light simmer and let it cook for 15 to 30 minutes (until it gets to your desired thickness). Stir every few minutes. Adjust the salt as needed.
Step 3: Storage
Pour the cooled sauce into a clean glass jar or into a squeeze bottle. Like with any soup or sauce it'll taste better after a day or two as the salt and spices blend.