Locking #BNB or #ETH for Network Fee

Is it possible to lock or allocate a certain amount of BNB or ETH for network fees in Trust wallet’s settings?

Yes, I know I can just sell some of my coins to get some BNB, but I usually prefer to hodl them since some of the coins lost their value. Then I need to buy or transfer BNB from another exchange which takes just a few minutes, but it would still be beneficial to have a certain allocation of BNB just for network fees.