By default, Samourai Wallet errs on the side of increasing the blockchain privacy and plausible deniability of transactions. This focus has a side effect of increasing in the size of transactions created, thus increasing the overall cost of the miner fee when sending. The wallet can be fully configured for creating low fee transactions by following the steps shown below.
Step 1 - Open settings
Tap the three vertical dots on the top right of the toolbar and then tap Settings. This will launch the wallet settings screen, where all configuration will take place.
Step 2 - Disable like-typed outputs
From the main Settings screen tap the Transactions option. Disable the Receive change to like-typed outputs option by removing the checkmark from the checkbox. Like-typed outputs is a Samourai feature that improves your privacy on the blockchain.
Step 3 - Disable STONEWALL
STONEWALL is enabled by default for all transactions. You can disable STONEWALL when sending a transaction, on a per-transaction-basis, by toggling the STONEWALL toggle switch to the OFF position.
The toggle switch for STONEWALL is located on the Review Transaction screen, which is accessed by tapping the blue Review Transaction button on the bottom of the Send Screen in Samourai.
Disabling STONEWALL will result in much smaller transactions, at the loss of blockchain privacy.
Step 4 - Enable RBF
From the Transactions settings screen Enable the Spend using RBF option by adding a checkmark to the checkbox. Enabling RBF will allow you to later top-up low transaction fees.
The wallet is now properly configured for creating low fee transactions at the sacrifice of some privacy and plausible deniability gains.